diff --git a/doc/sources/index.rst b/doc/sources/index.rst
index e3205dae..c8f688d3 100644
--- a/doc/sources/index.rst
+++ b/doc/sources/index.rst
@@ -51,3 +51,4 @@ Resources
 
 * HTTP/2 https://tools.ietf.org/html/rfc7540
 * HPACK https://tools.ietf.org/html/rfc7541
+* HTTP Alternative Services https://tools.ietf.org/html/rfc7838
diff --git a/lib/includes/nghttp2/nghttp2.h b/lib/includes/nghttp2/nghttp2.h
index 8cd00ca6..c9609051 100644
--- a/lib/includes/nghttp2/nghttp2.h
+++ b/lib/includes/nghttp2/nghttp2.h
@@ -591,7 +591,12 @@ typedef enum {
    * callbacks because the library processes this frame type and its
    * preceding HEADERS/PUSH_PROMISE as a single frame.
    */
-  NGHTTP2_CONTINUATION = 0x09
+  NGHTTP2_CONTINUATION = 0x09,
+  /**
+   * The ALTSVC frame, which is defined in `RFC 7383
+   * <https://tools.ietf.org/html/rfc7838#section-4>`_.
+   */
+  NGHTTP2_ALTSVC = 0x0a
 } nghttp2_frame_type;
 
 /**
@@ -2373,6 +2378,26 @@ NGHTTP2_EXTERN void
 nghttp2_option_set_user_recv_extension_type(nghttp2_option *option,
                                             uint8_t type);
 
+/**
+ * @function
+ *
+ * Sets extension frame type the application is willing to receive
+ * using builtin handler.  The |type| is the extension frame type to
+ * receive, and must be strictly greater than 0x9.  Otherwise, this
+ * function does nothing.  The application can call this function
+ * multiple times to set more than one frame type to receive.  The
+ * application does not have to call this function if it just sends
+ * extension frames.
+ *
+ * If same frame type is passed to both
+ * `nghttp2_option_set_builtin_recv_extension_type()` and
+ * `nghttp2_option_set_user_recv_extension_type()`, the latter takes
+ * precedence.
+ */
+NGHTTP2_EXTERN void
+nghttp2_option_set_builtin_recv_extension_type(nghttp2_option *option,
+                                               uint8_t type);
+
 /**
  * @function
  *
@@ -4113,6 +4138,80 @@ NGHTTP2_EXTERN int nghttp2_submit_extension(nghttp2_session *session,
                                             uint8_t type, uint8_t flags,
                                             int32_t stream_id, void *payload);
 
+/**
+ * @struct
+ *
+ * The payload of ALTSVC frame.  ALTSVC frame is a non-critical
+ * extension to HTTP/2.  If this frame is received, and
+ * `nghttp2_option_set_user_recv_extension_type()` is not set, and
+ * `nghttp2_option_set_builtin_recv_extension_type()` is set for
+ * :enum:`NGHTTP2_ALTSVC`, ``nghttp2_extension.payload`` will point to
+ * this struct.
+ *
+ * It has the following members:
+ */
+typedef struct {
+  /**
+   * The pointer to origin which this alternative service is
+   * associated with.  This is not necessarily NULL-terminated.
+   */
+  uint8_t *origin;
+  /**
+   * The length of the |origin|.
+   */
+  size_t origin_len;
+  /**
+   * The pointer to Alt-Svc field value contained in ALTSVC frame.
+   * This is not necessarily NULL-terminated.
+   */
+  uint8_t *field_value;
+  /**
+   * The length of the |field_value|.
+   */
+  size_t field_value_len;
+} nghttp2_ext_altsvc;
+
+/**
+ * @function
+ *
+ * Submits ALTSVC frame.
+ *
+ * ALTSVC frame is a non-critical extension to HTTP/2, and defined in
+ * is defined in `RFC 7383
+ * <https://tools.ietf.org/html/rfc7838#section-4>`_.
+ *
+ * The |flags| is currently ignored and should be
+ * :enum:`NGHTTP2_FLAG_NONE`.
+ *
+ * The |origin| points to the origin this alternative service is
+ * associated with.  The |origin_len| is the length of the origin.  If
+ * |stream_id| is 0, the origin must be specified.  If |stream_id| is
+ * not zero, the origin must be empty (in other words, |origin_len|
+ * must be 0).
+ *
+ * The ALTSVC frame is only usable from server side.  If this function
+ * is invoked with client side session, this function returns
+ * :enum:`NGHTTP2_ERR_INVALID_STATE`.
+ *
+ * This function returns 0 if it succeeds, or one of the following
+ * negative error codes:
+ *
+ * :enum:`NGHTTP2_ERR_NOMEM`
+ *     Out of memory
+ * :enum:`NGHTTP2_ERR_INVALID_STATE`
+ *     The function is called from client side session
+ * :enum:`NGHTTP2_ERR_INVALID_ARGUMENT`
+ *     The sum of |origin_len| and |field_value_len| is larger than
+ *     16382; or |origin_len| is 0 while |stream_id| is 0; or
+ *     |origin_len| is not 0 while |stream_id| is not 0.
+ */
+NGHTTP2_EXTERN int nghttp2_submit_altsvc(nghttp2_session *session,
+                                         uint8_t flags, int32_t stream_id,
+                                         const uint8_t *origin,
+                                         size_t origin_len,
+                                         const uint8_t *field_value,
+                                         size_t field_value_len);
+
 /**
  * @function
  *
diff --git a/lib/nghttp2_frame.c b/lib/nghttp2_frame.c
index 3d057847..b4c1d443 100644
--- a/lib/nghttp2_frame.c
+++ b/lib/nghttp2_frame.c
@@ -193,6 +193,30 @@ void nghttp2_frame_extension_init(nghttp2_extension *frame, uint8_t type,
 
 void nghttp2_frame_extension_free(nghttp2_extension *frame _U_) {}
 
+void nghttp2_frame_altsvc_init(nghttp2_extension *frame, int32_t stream_id,
+                               uint8_t *origin, size_t origin_len,
+                               uint8_t *field_value, size_t field_value_len) {
+  nghttp2_ext_altsvc *altsvc;
+
+  nghttp2_frame_hd_init(&frame->hd, 2 + origin_len + field_value_len,
+                        NGHTTP2_ALTSVC, NGHTTP2_FLAG_NONE, stream_id);
+
+  altsvc = frame->payload;
+  altsvc->origin = origin;
+  altsvc->origin_len = origin_len;
+  altsvc->field_value = field_value;
+  altsvc->field_value_len = field_value_len;
+}
+
+void nghttp2_frame_altsvc_free(nghttp2_extension *frame, nghttp2_mem *mem) {
+  nghttp2_ext_altsvc *altsvc;
+
+  altsvc = frame->payload;
+  /* We use the same buffer for altsvc->origin and
+     altsvc->field_value. */
+  nghttp2_mem_free(mem, altsvc->origin);
+}
+
 size_t nghttp2_frame_priority_len(uint8_t flags) {
   if (flags & NGHTTP2_FLAG_PRIORITY) {
     return NGHTTP2_PRIORITY_SPECLEN;
@@ -668,6 +692,55 @@ void nghttp2_frame_unpack_window_update_payload(nghttp2_window_update *frame,
       nghttp2_get_uint32(payload) & NGHTTP2_WINDOW_SIZE_INCREMENT_MASK;
 }
 
+int nghttp2_frame_pack_altsvc(nghttp2_bufs *bufs, nghttp2_extension *frame) {
+  int rv;
+  nghttp2_buf *buf;
+  nghttp2_ext_altsvc *altsvc;
+
+  altsvc = frame->payload;
+
+  buf = &bufs->head->buf;
+
+  assert(nghttp2_buf_avail(buf) >=
+         2 + altsvc->origin_len + altsvc->field_value_len);
+
+  buf->pos -= NGHTTP2_FRAME_HDLEN;
+
+  nghttp2_frame_pack_frame_hd(buf->pos, &frame->hd);
+
+  nghttp2_put_uint16be(buf->last, (uint16_t)altsvc->origin_len);
+  buf->last += 2;
+
+  rv = nghttp2_bufs_add(bufs, altsvc->origin, altsvc->origin_len);
+
+  assert(rv == 0);
+
+  rv = nghttp2_bufs_add(bufs, altsvc->field_value, altsvc->field_value_len);
+
+  assert(rv == 0);
+
+  return 0;
+}
+
+void nghttp2_frame_unpack_altsvc_payload(nghttp2_extension *frame,
+                                         size_t origin_len, uint8_t *payload,
+                                         size_t payloadlen) {
+  nghttp2_ext_altsvc *altsvc;
+  uint8_t *p;
+
+  altsvc = frame->payload;
+  p = payload;
+
+  altsvc->origin = p;
+
+  p += origin_len;
+
+  altsvc->origin_len = origin_len;
+
+  altsvc->field_value = p;
+  altsvc->field_value_len = (size_t)(payload + payloadlen - p);
+}
+
 nghttp2_settings_entry *nghttp2_frame_iv_copy(const nghttp2_settings_entry *iv,
                                               size_t niv, nghttp2_mem *mem) {
   nghttp2_settings_entry *iv_copy;
diff --git a/lib/nghttp2_frame.h b/lib/nghttp2_frame.h
index fa0eb452..c6111728 100644
--- a/lib/nghttp2_frame.h
+++ b/lib/nghttp2_frame.h
@@ -72,7 +72,7 @@
 #define NGHTTP2_MAX_PADLEN 256
 
 /* Union of extension frame payload */
-typedef union { int dummy; } nghttp2_ext_frame_payload;
+typedef union { nghttp2_ext_altsvc altsvc; } nghttp2_ext_frame_payload;
 
 void nghttp2_frame_pack_frame_hd(uint8_t *buf, const nghttp2_frame_hd *hd);
 
@@ -367,6 +367,27 @@ void nghttp2_frame_unpack_window_update_payload(nghttp2_window_update *frame,
                                                 const uint8_t *payload,
                                                 size_t payloadlen);
 
+/*
+ * Packs ALTSVC frame |frame| in wire frame format and store it in
+ * |bufs|.
+ *
+ * The caller must make sure that nghttp2_bufs_reset(bufs) is called
+ * before calling this function.
+ *
+ * This function always succeeds and returns 0.
+ */
+int nghttp2_frame_pack_altsvc(nghttp2_bufs *bufs, nghttp2_extension *ext);
+
+/*
+ * Unpacks ALTSVC wire format into |frame|.  The |payload| of
+ * |payloadlen| bytes contains frame payload.  This function assumes
+ * that frame->payload points to the nghttp2_ext_altsvc object.
+ *
+ * This function always succeeds and returns 0.
+ */
+void nghttp2_frame_unpack_altsvc_payload(nghttp2_extension *frame,
+                                         size_t origin_len, uint8_t *payload,
+                                         size_t payloadlen);
 /*
  * Initializes HEADERS frame |frame| with given values.  |frame| takes
  * ownership of |nva|, so caller must not free it. If |stream_id| is
@@ -445,6 +466,25 @@ void nghttp2_frame_extension_init(nghttp2_extension *frame, uint8_t type,
 
 void nghttp2_frame_extension_free(nghttp2_extension *frame);
 
+/*
+ * Initializes ALTSVC frame |frame| with given values.  This function
+ * assumes that frame->payload points to nghttp2_ext_altsvc object.
+ * Also |origin| and |field_value| are allocated in single buffer,
+ * starting |origin|.  On success, this function takes ownership of
+ * |origin|, so caller must not free it.
+ */
+void nghttp2_frame_altsvc_init(nghttp2_extension *frame, int32_t stream_id,
+                               uint8_t *origin, size_t origin_len,
+                               uint8_t *field_value, size_t field_value_len);
+
+/*
+ * Frees up resources under |frame|.  This function does not free
+ * nghttp2_ext_altsvc object pointed by frame->payload.  This function
+ * only frees origin pointed by nghttp2_ext_altsvc.origin.  Therefore,
+ * other fields must be allocated in the same buffer with origin.
+ */
+void nghttp2_frame_altsvc_free(nghttp2_extension *frame, nghttp2_mem *mem);
+
 /*
  * Returns the number of padding bytes after payload.  The total
  * padding length is given in the |padlen|.  The returned value does
diff --git a/lib/nghttp2_option.c b/lib/nghttp2_option.c
index e3e8717b..e8d6ed16 100644
--- a/lib/nghttp2_option.c
+++ b/lib/nghttp2_option.c
@@ -24,6 +24,8 @@
  */
 #include "nghttp2_option.h"
 
+#include "nghttp2_session.h"
+
 int nghttp2_option_new(nghttp2_option **option_ptr) {
   *option_ptr = calloc(1, sizeof(nghttp2_option));
 
@@ -63,6 +65,10 @@ void nghttp2_option_set_max_reserved_remote_streams(nghttp2_option *option,
   option->max_reserved_remote_streams = val;
 }
 
+static void set_ext_type(uint8_t *ext_types, uint8_t type) {
+  ext_types[type / 8] = (uint8_t)(ext_types[type / 8] | (1 << (type & 0x7)));
+}
+
 void nghttp2_option_set_user_recv_extension_type(nghttp2_option *option,
                                                  uint8_t type) {
   if (type < 10) {
@@ -70,8 +76,19 @@ void nghttp2_option_set_user_recv_extension_type(nghttp2_option *option,
   }
 
   option->opt_set_mask |= NGHTTP2_OPT_USER_RECV_EXT_TYPES;
-  option->user_recv_ext_types[type / 8] =
-      (uint8_t)(option->user_recv_ext_types[type / 8] | (1 << (type & 0x7)));
+  set_ext_type(option->user_recv_ext_types, type);
+}
+
+void nghttp2_option_set_builtin_recv_extension_type(nghttp2_option *option,
+                                                    uint8_t type) {
+  switch (type) {
+  case NGHTTP2_ALTSVC:
+    option->opt_set_mask |= NGHTTP2_OPT_BUILTIN_RECV_EXT_TYPES;
+    option->builtin_recv_ext_types |= NGHTTP2_TYPEMASK_ALTSVC;
+    return;
+  default:
+    return;
+  }
 }
 
 void nghttp2_option_set_no_auto_ping_ack(nghttp2_option *option, int val) {
diff --git a/lib/nghttp2_option.h b/lib/nghttp2_option.h
index f859b4eb..87ef4e04 100644
--- a/lib/nghttp2_option.h
+++ b/lib/nghttp2_option.h
@@ -61,7 +61,8 @@ typedef enum {
   NGHTTP2_OPT_NO_HTTP_MESSAGING = 1 << 3,
   NGHTTP2_OPT_MAX_RESERVED_REMOTE_STREAMS = 1 << 4,
   NGHTTP2_OPT_USER_RECV_EXT_TYPES = 1 << 5,
-  NGHTTP2_OPT_NO_AUTO_PING_ACK = 1 << 6
+  NGHTTP2_OPT_NO_AUTO_PING_ACK = 1 << 6,
+  NGHTTP2_OPT_BUILTIN_RECV_EXT_TYPES = 1 << 7
 } nghttp2_option_flag;
 
 /**
@@ -81,6 +82,10 @@ struct nghttp2_option {
    * NGHTTP2_OPT_MAX_RESERVED_REMOTE_STREAMS
    */
   uint32_t max_reserved_remote_streams;
+  /**
+   * NGHTTP2_OPT_BUILTIN_RECV_EXT_TYPES
+   */
+  uint32_t builtin_recv_ext_types;
   /**
    * NGHTTP2_OPT_NO_AUTO_WINDOW_UPDATE
    */
diff --git a/lib/nghttp2_outbound_item.c b/lib/nghttp2_outbound_item.c
index 886f330c..1633cc36 100644
--- a/lib/nghttp2_outbound_item.c
+++ b/lib/nghttp2_outbound_item.c
@@ -72,9 +72,25 @@ void nghttp2_outbound_item_free(nghttp2_outbound_item *item, nghttp2_mem *mem) {
   case NGHTTP2_WINDOW_UPDATE:
     nghttp2_frame_window_update_free(&frame->window_update);
     break;
-  default:
-    nghttp2_frame_extension_free(&frame->ext);
-    break;
+  default: {
+    nghttp2_ext_aux_data *aux_data;
+
+    aux_data = &item->aux_data.ext;
+
+    if (aux_data->builtin == 0) {
+      nghttp2_frame_extension_free(&frame->ext);
+      break;
+    }
+
+    switch (frame->hd.type) {
+    case NGHTTP2_ALTSVC:
+      nghttp2_frame_altsvc_free(&frame->ext, mem);
+      break;
+    default:
+      assert(0);
+      break;
+    }
+  }
   }
 }
 
diff --git a/lib/nghttp2_outbound_item.h b/lib/nghttp2_outbound_item.h
index f1daeb1c..8bda776b 100644
--- a/lib/nghttp2_outbound_item.h
+++ b/lib/nghttp2_outbound_item.h
@@ -87,11 +87,19 @@ typedef struct {
   uint8_t flags;
 } nghttp2_goaway_aux_data;
 
+/* struct used for extension frame */
+typedef struct {
+  /* nonzero if this extension frame is serialized by library
+     function, instead of user-defined callbacks. */
+  uint8_t builtin;
+} nghttp2_ext_aux_data;
+
 /* Additional data which cannot be stored in nghttp2_frame struct */
 typedef union {
   nghttp2_data_aux_data data;
   nghttp2_headers_aux_data headers;
   nghttp2_goaway_aux_data goaway;
+  nghttp2_ext_aux_data ext;
 } nghttp2_aux_data;
 
 struct nghttp2_outbound_item;
@@ -99,6 +107,9 @@ typedef struct nghttp2_outbound_item nghttp2_outbound_item;
 
 struct nghttp2_outbound_item {
   nghttp2_frame frame;
+  /* Storage for extension frame payload.  frame->ext.payload points
+     to this structure to avoid frequent memory allocation. */
+  nghttp2_ext_frame_payload ext_frame_payload;
   nghttp2_aux_data aux_data;
   /* The priority used in priority comparion.  Smaller is served
      ealier.  For PING, SETTINGS and non-DATA frames (excluding
diff --git a/lib/nghttp2_session.c b/lib/nghttp2_session.c
index 84845abf..d859e2fb 100644
--- a/lib/nghttp2_session.c
+++ b/lib/nghttp2_session.c
@@ -142,6 +142,10 @@ static int session_detect_idle_stream(nghttp2_session *session,
   return 0;
 }
 
+static int check_ext_type_set(const uint8_t *ext_types, uint8_t type) {
+  return (ext_types[type / 8] & (1 << (type & 0x7))) > 0;
+}
+
 static int session_call_error_callback(nghttp2_session *session,
                                        const char *fmt, ...) {
   size_t bufsize;
@@ -316,7 +320,20 @@ static void session_inbound_frame_reset(nghttp2_session *session) {
     break;
   default:
     /* extension frame */
-    nghttp2_frame_extension_free(&iframe->frame.ext);
+    if (check_ext_type_set(session->user_recv_ext_types,
+                           iframe->frame.hd.type)) {
+      nghttp2_frame_extension_free(&iframe->frame.ext);
+    } else {
+      switch (iframe->frame.hd.type) {
+      case NGHTTP2_ALTSVC:
+        if ((session->builtin_recv_ext_types & NGHTTP2_TYPEMASK_ALTSVC) == 0) {
+          break;
+        }
+        nghttp2_frame_altsvc_free(&iframe->frame.ext, mem);
+        break;
+      }
+    }
+
     break;
   }
 
@@ -332,6 +349,8 @@ static void session_inbound_frame_reset(nghttp2_session *session) {
   nghttp2_buf_free(&iframe->lbuf, mem);
   nghttp2_buf_wrap_init(&iframe->lbuf, NULL, 0);
 
+  iframe->raw_lbuf = NULL;
+
   iframe->niv = 0;
   iframe->payloadleft = 0;
   iframe->padlen = 0;
@@ -474,6 +493,10 @@ static int session_new(nghttp2_session **session_ptr,
              sizeof((*session_ptr)->user_recv_ext_types));
     }
 
+    if (option->opt_set_mask & NGHTTP2_OPT_BUILTIN_RECV_EXT_TYPES) {
+      (*session_ptr)->builtin_recv_ext_types = option->builtin_recv_ext_types;
+    }
+
     if ((option->opt_set_mask & NGHTTP2_OPT_NO_AUTO_PING_ACK) &&
         option->no_auto_ping_ack) {
       (*session_ptr)->opt_flags |= NGHTTP2_OPTMASK_NO_AUTO_PING_ACK;
@@ -1664,6 +1687,26 @@ static int session_predicate_window_update_send(nghttp2_session *session,
   return 0;
 }
 
+static int session_predicate_altsvc_send(nghttp2_session *session,
+                                         int32_t stream_id) {
+  nghttp2_stream *stream;
+
+  if (session_is_closing(session)) {
+    return NGHTTP2_ERR_SESSION_CLOSING;
+  }
+
+  if (stream_id == 0) {
+    return 0;
+  }
+
+  stream = nghttp2_session_get_stream(session, stream_id);
+  if (stream == NULL) {
+    return NGHTTP2_ERR_STREAM_CLOSED;
+  }
+
+  return 0;
+}
+
 /* Take into account settings max frame size and both connection-level
    flow control here */
 static ssize_t
@@ -2103,19 +2146,45 @@ static int session_prep_frame(nghttp2_session *session,
       /* We never handle CONTINUATION here. */
       assert(0);
       break;
-    default:
+    default: {
+      nghttp2_ext_aux_data *aux_data;
+
       /* extension frame */
-      if (session_is_closing(session)) {
-        return NGHTTP2_ERR_SESSION_CLOSING;
+
+      aux_data = &item->aux_data.ext;
+
+      if (aux_data->builtin == 0) {
+        if (session_is_closing(session)) {
+          return NGHTTP2_ERR_SESSION_CLOSING;
+        }
+
+        rv = session_pack_extension(session, &session->aob.framebufs, frame);
+        if (rv != 0) {
+          return rv;
+        }
+
+        break;
       }
 
-      rv = session_pack_extension(session, &session->aob.framebufs, frame);
-      if (rv != 0) {
-        return rv;
+      switch (frame->hd.type) {
+      case NGHTTP2_ALTSVC:
+        rv = session_predicate_altsvc_send(session, frame->hd.stream_id);
+        if (rv != 0) {
+          return rv;
+        }
+
+        nghttp2_frame_pack_altsvc(&session->aob.framebufs, &frame->ext);
+
+        break;
+      default:
+        /* Unreachable here */
+        assert(0);
+        break;
       }
 
       break;
     }
+    }
     return 0;
   } else {
     size_t next_readmax;
@@ -4591,6 +4660,52 @@ static int session_process_window_update_frame(nghttp2_session *session) {
   return nghttp2_session_on_window_update_received(session, frame);
 }
 
+int nghttp2_session_on_altsvc_received(nghttp2_session *session,
+                                       nghttp2_frame *frame) {
+  nghttp2_ext_altsvc *altsvc;
+  nghttp2_stream *stream;
+
+  altsvc = frame->ext.payload;
+
+  /* session->server case has been excluded */
+
+  if (frame->hd.stream_id == 0) {
+    if (altsvc->origin_len == 0) {
+      return 0;
+    }
+  } else {
+    if (altsvc->origin_len > 0) {
+      return 0;
+    }
+
+    stream = nghttp2_session_get_stream(session, frame->hd.stream_id);
+    if (!stream) {
+      return 0;
+    }
+
+    if (stream->state == NGHTTP2_STREAM_CLOSING) {
+      return 0;
+    }
+  }
+
+  return session_call_on_frame_received(session, frame);
+}
+
+static int session_process_altsvc_frame(nghttp2_session *session) {
+  nghttp2_inbound_frame *iframe = &session->iframe;
+  nghttp2_frame *frame = &iframe->frame;
+
+  nghttp2_frame_unpack_altsvc_payload(
+      &frame->ext, nghttp2_get_uint16(iframe->sbuf.pos), iframe->lbuf.pos,
+      nghttp2_buf_len(&iframe->lbuf));
+
+  /* nghttp2_frame_unpack_altsvc_payload steals buffer from
+     iframe->lbuf */
+  nghttp2_buf_wrap_init(&iframe->lbuf, NULL, 0);
+
+  return nghttp2_session_on_altsvc_received(session, frame);
+}
+
 static int session_process_extension_frame(nghttp2_session *session) {
   int rv;
   nghttp2_inbound_frame *iframe = &session->iframe;
@@ -5434,25 +5549,66 @@ ssize_t nghttp2_session_mem_recv(nghttp2_session *session, const uint8_t *in,
 
         break;
       default:
-        DEBUGF(fprintf(stderr, "recv: unknown frame\n"));
+        DEBUGF(fprintf(stderr, "recv: extension frame\n"));
 
-        if (!session->callbacks.unpack_extension_callback ||
-            (session->user_recv_ext_types[iframe->frame.hd.type / 8] &
-             (1 << (iframe->frame.hd.type & 0x7))) == 0) {
-          /* Silently ignore unknown frame type. */
+        if (check_ext_type_set(session->user_recv_ext_types,
+                               iframe->frame.hd.type)) {
+          if (!session->callbacks.unpack_extension_callback) {
+            /* Silently ignore unknown frame type. */
+
+            busy = 1;
+
+            iframe->state = NGHTTP2_IB_IGN_PAYLOAD;
+
+            break;
+          }
 
           busy = 1;
 
-          iframe->state = NGHTTP2_IB_IGN_PAYLOAD;
+          iframe->state = NGHTTP2_IB_READ_EXTENSION_PAYLOAD;
 
           break;
+        } else {
+          switch (iframe->frame.hd.type) {
+          case NGHTTP2_ALTSVC:
+            if ((session->builtin_recv_ext_types & NGHTTP2_TYPEMASK_ALTSVC) ==
+                0) {
+              busy = 1;
+              iframe->state = NGHTTP2_IB_IGN_PAYLOAD;
+              break;
+            }
+
+            DEBUGF(fprintf(stderr, "recv: ALTSVC\n"));
+
+            iframe->frame.hd.flags = NGHTTP2_FLAG_NONE;
+            iframe->frame.ext.payload = &iframe->ext_frame_payload.altsvc;
+
+            if (session->server) {
+              busy = 1;
+              iframe->state = NGHTTP2_IB_IGN_PAYLOAD;
+              break;
+            }
+
+            if (iframe->payloadleft < 2) {
+              busy = 1;
+              iframe->state = NGHTTP2_IB_FRAME_SIZE_ERROR;
+              break;
+            }
+
+            busy = 1;
+
+            iframe->state = NGHTTP2_IB_READ_NBYTE;
+            inbound_frame_set_mark(iframe, 2);
+
+            break;
+          default:
+            busy = 1;
+
+            iframe->state = NGHTTP2_IB_IGN_PAYLOAD;
+
+            break;
+          }
         }
-
-        busy = 1;
-
-        iframe->state = NGHTTP2_IB_READ_EXTENSION_PAYLOAD;
-
-        break;
       }
 
       if (!on_begin_frame_called) {
@@ -5662,6 +5818,37 @@ ssize_t nghttp2_session_mem_recv(nghttp2_session *session, const uint8_t *in,
         session_inbound_frame_reset(session);
 
         break;
+      case NGHTTP2_ALTSVC: {
+        size_t origin_len;
+
+        origin_len = nghttp2_get_uint16(iframe->sbuf.pos);
+
+        DEBUGF(fprintf(stderr, "recv: origin_len=%zu\n", origin_len));
+
+        if (2 + origin_len > iframe->payloadleft) {
+          busy = 1;
+          iframe->state = NGHTTP2_IB_FRAME_SIZE_ERROR;
+          break;
+        }
+
+        if (iframe->frame.hd.length > 2) {
+          iframe->raw_lbuf =
+              nghttp2_mem_malloc(mem, iframe->frame.hd.length - 2);
+
+          if (iframe->raw_lbuf == NULL) {
+            return NGHTTP2_ERR_NOMEM;
+          }
+
+          nghttp2_buf_wrap_init(&iframe->lbuf, iframe->raw_lbuf,
+                                iframe->frame.hd.length);
+        }
+
+        busy = 1;
+
+        iframe->state = NGHTTP2_IB_READ_ALTSVC_PAYLOAD;
+
+        break;
+      }
       default:
         /* This is unknown frame */
         session_inbound_frame_reset(session);
@@ -6187,6 +6374,36 @@ ssize_t nghttp2_session_mem_recv(nghttp2_session *session, const uint8_t *in,
 
       session_inbound_frame_reset(session);
 
+      break;
+    case NGHTTP2_IB_READ_ALTSVC_PAYLOAD:
+      DEBUGF(fprintf(stderr, "recv: [IB_READ_ALTSVC_PAYLOAD]\n"));
+
+      readlen = inbound_frame_payload_readlen(iframe, in, last);
+
+      if (readlen > 0) {
+        iframe->lbuf.last = nghttp2_cpymem(iframe->lbuf.last, in, readlen);
+
+        iframe->payloadleft -= readlen;
+        in += readlen;
+      }
+
+      DEBUGF(fprintf(stderr, "recv: readlen=%zu, payloadleft=%zu\n", readlen,
+                     iframe->payloadleft));
+
+      if (iframe->payloadleft) {
+        assert(nghttp2_buf_avail(&iframe->lbuf) > 0);
+
+        break;
+      }
+
+      rv = session_process_altsvc_frame(session);
+
+      if (nghttp2_is_fatal(rv)) {
+        return rv;
+      }
+
+      session_inbound_frame_reset(session);
+
       break;
     }
 
diff --git a/lib/nghttp2_session.h b/lib/nghttp2_session.h
index 3c3764de..a5cb1aec 100644
--- a/lib/nghttp2_session.h
+++ b/lib/nghttp2_session.h
@@ -54,6 +54,15 @@ typedef enum {
   NGHTTP2_OPTMASK_NO_AUTO_PING_ACK = 1 << 3
 } nghttp2_optmask;
 
+/*
+ * bitmask for built-in type to enable the default handling for that
+ * type of the frame.
+ */
+typedef enum {
+  NGHTTP2_TYPEMASK_NONE = 0,
+  NGHTTP2_TYPEMASK_ALTSVC = 1 << 0
+} nghttp2_typemask;
+
 typedef enum {
   NGHTTP2_OB_POP_ITEM,
   NGHTTP2_OB_SEND_DATA,
@@ -107,6 +116,7 @@ typedef enum {
   NGHTTP2_IB_READ_DATA,
   NGHTTP2_IB_IGN_DATA,
   NGHTTP2_IB_IGN_ALL,
+  NGHTTP2_IB_READ_ALTSVC_PAYLOAD,
   NGHTTP2_IB_READ_EXTENSION_PAYLOAD
 } nghttp2_inbound_state;
 
@@ -294,6 +304,9 @@ struct nghttp2_session {
   /* Unacked local SETTINGS_MAX_CONCURRENT_STREAMS value. We use this
      to refuse the incoming stream if it exceeds this value. */
   uint32_t pending_local_max_concurrent_stream;
+  /* The bitwose OR of zero or more of nghttp2_typemask to indicate
+     that the default handling of extension frame is enabled. */
+  uint32_t builtin_recv_ext_types;
   /* Unacked local ENABLE_PUSH value.  We use this to refuse
      PUSH_PROMISE before SETTINGS ACK is received. */
   uint8_t pending_enable_push;
@@ -716,6 +729,19 @@ int nghttp2_session_on_goaway_received(nghttp2_session *session,
 int nghttp2_session_on_window_update_received(nghttp2_session *session,
                                               nghttp2_frame *frame);
 
+/*
+ * Called when ALTSVC is recieved, assuming |frame| is properly
+ * initialized.
+ *
+ * This function returns 0 if it succeeds, or one of the following
+ * negative error codes:
+ *
+ * NGHTTP2_ERR_CALLBACK_FAILURE
+ *   The callback function failed.
+ */
+int nghttp2_session_on_altsvc_received(nghttp2_session *session,
+                                       nghttp2_frame *frame);
+
 /*
  * Called when DATA is received, assuming |frame| is properly
  * initialized.
diff --git a/lib/nghttp2_submit.c b/lib/nghttp2_submit.c
index 9c11e210..6329334c 100644
--- a/lib/nghttp2_submit.c
+++ b/lib/nghttp2_submit.c
@@ -410,6 +410,90 @@ int nghttp2_submit_window_update(nghttp2_session *session, uint8_t flags,
   return 0;
 }
 
+int nghttp2_submit_altsvc(nghttp2_session *session, uint8_t flags _U_,
+                          int32_t stream_id, const uint8_t *origin,
+                          size_t origin_len, const uint8_t *field_value,
+                          size_t field_value_len) {
+  nghttp2_mem *mem;
+  uint8_t *buf, *p;
+  uint8_t *origin_copy;
+  uint8_t *field_value_copy;
+  nghttp2_outbound_item *item;
+  nghttp2_frame *frame;
+  nghttp2_ext_altsvc *altsvc;
+  int rv;
+
+  mem = &session->mem;
+
+  if (!session->server) {
+    return NGHTTP2_ERR_INVALID_STATE;
+  }
+
+  if (2 + origin_len + field_value_len > NGHTTP2_MAX_PAYLOADLEN) {
+    return NGHTTP2_ERR_INVALID_ARGUMENT;
+  }
+
+  if (stream_id == 0) {
+    if (origin_len == 0) {
+      return NGHTTP2_ERR_INVALID_ARGUMENT;
+    }
+  } else if (origin_len != 0) {
+    return NGHTTP2_ERR_INVALID_ARGUMENT;
+  }
+
+  buf = nghttp2_mem_malloc(mem, origin_len + field_value_len + 2);
+  if (buf == NULL) {
+    return NGHTTP2_ERR_NOMEM;
+  }
+
+  p = buf;
+
+  origin_copy = p;
+  if (origin_len) {
+    p = nghttp2_cpymem(p, origin, origin_len);
+  }
+  *p++ = '\0';
+
+  field_value_copy = p;
+  if (field_value_len) {
+    p = nghttp2_cpymem(p, field_value, field_value_len);
+  }
+  *p++ = '\0';
+
+  item = nghttp2_mem_malloc(mem, sizeof(nghttp2_outbound_item));
+  if (item == NULL) {
+    rv = NGHTTP2_ERR_NOMEM;
+    goto fail_item_malloc;
+  }
+
+  nghttp2_outbound_item_init(item);
+
+  item->aux_data.ext.builtin = 1;
+
+  altsvc = &item->ext_frame_payload.altsvc;
+
+  frame = &item->frame;
+  frame->ext.payload = altsvc;
+
+  nghttp2_frame_altsvc_init(&frame->ext, stream_id, origin_copy, origin_len,
+                            field_value_copy, field_value_len);
+
+  rv = nghttp2_session_add_item(session, item);
+  if (rv != 0) {
+    nghttp2_frame_altsvc_free(&frame->ext, mem);
+    nghttp2_mem_free(mem, item);
+
+    return rv;
+  }
+
+  return 0;
+
+fail_item_malloc:
+  free(buf);
+
+  return rv;
+}
+
 static uint8_t set_request_flags(const nghttp2_priority_spec *pri_spec,
                                  const nghttp2_data_provider *data_prd) {
   uint8_t flags = NGHTTP2_FLAG_NONE;
diff --git a/src/app_helper.cc b/src/app_helper.cc
index 603151cf..0b47b48c 100644
--- a/src/app_helper.cc
+++ b/src/app_helper.cc
@@ -104,6 +104,8 @@ std::string strframetype(uint8_t type) {
     return "GOAWAY";
   case NGHTTP2_WINDOW_UPDATE:
     return "WINDOW_UPDATE";
+  case NGHTTP2_ALTSVC:
+    return "ALTSVC";
   }
 
   std::string s = "extension(0x";
@@ -339,6 +341,14 @@ void print_frame(print_type ptype, const nghttp2_frame *frame) {
     fprintf(outfile, "(window_size_increment=%d)\n",
             frame->window_update.window_size_increment);
     break;
+  case NGHTTP2_ALTSVC: {
+    auto altsvc = static_cast<nghttp2_ext_altsvc *>(frame->ext.payload);
+    print_frame_attr_indent();
+    fprintf(outfile, "(origin=[%.*s], altsvc_field_value=[%.*s])\n",
+            static_cast<int>(altsvc->origin_len), altsvc->origin,
+            static_cast<int>(altsvc->field_value_len), altsvc->field_value);
+    break;
+  }
   default:
     break;
   }
diff --git a/src/nghttp.cc b/src/nghttp.cc
index e3647b17..42d25d74 100644
--- a/src/nghttp.cc
+++ b/src/nghttp.cc
@@ -118,6 +118,7 @@ Config::Config()
   nghttp2_option_new(&http2_option);
   nghttp2_option_set_peer_max_concurrent_streams(http2_option,
                                                  peer_max_concurrent_streams);
+  nghttp2_option_set_builtin_recv_extension_type(http2_option, NGHTTP2_ALTSVC);
 }
 
 Config::~Config() { nghttp2_option_del(http2_option); }
diff --git a/tests/failmalloc.c b/tests/failmalloc.c
index 472be317..f2734033 100644
--- a/tests/failmalloc.c
+++ b/tests/failmalloc.c
@@ -55,6 +55,8 @@ int main(int argc _U_, char *argv[] _U_) {
   /* add the tests to the suite */
   if (!CU_add_test(pSuite, "failmalloc_session_send",
                    test_nghttp2_session_send) ||
+      !CU_add_test(pSuite, "failmalloc_session_send_server",
+                   test_nghttp2_session_send_server) ||
       !CU_add_test(pSuite, "failmalloc_session_recv",
                    test_nghttp2_session_recv) ||
       !CU_add_test(pSuite, "failmalloc_frame", test_nghttp2_frame) ||
diff --git a/tests/failmalloc_test.c b/tests/failmalloc_test.c
index 923975b0..9869611d 100644
--- a/tests/failmalloc_test.c
+++ b/tests/failmalloc_test.c
@@ -217,6 +217,50 @@ void test_nghttp2_session_send(void) {
   TEST_FAILMALLOC_RUN(run_nghttp2_session_send);
 }
 
+static void run_nghttp2_session_send_server(void) {
+  nghttp2_session *session;
+  nghttp2_session_callbacks *callbacks;
+  int rv;
+  const uint8_t *txdata;
+  ssize_t txdatalen;
+  rv = nghttp2_session_callbacks_new(&callbacks);
+  if (rv != 0) {
+    return;
+  }
+
+  rv = nghttp2_session_server_new3(&session, callbacks, NULL, NULL,
+                                   nghttp2_mem_fm());
+
+  nghttp2_session_callbacks_del(callbacks);
+
+  if (rv != 0) {
+    return;
+  }
+
+  const uint8_t origin[] = "nghttp2.org";
+  const uint8_t altsvc_field_value[] = "h2=\":443\"";
+
+  rv = nghttp2_submit_altsvc(session, NGHTTP2_FLAG_NONE, 0, origin,
+                             sizeof(origin) - 1, altsvc_field_value,
+                             sizeof(altsvc_field_value) - 1);
+  if (rv != 0) {
+    goto fail;
+  }
+
+  txdatalen = nghttp2_session_mem_send(session, &txdata);
+
+  if (txdatalen < 0) {
+    goto fail;
+  }
+
+fail:
+   nghttp2_session_del(session);
+}
+
+void test_nghttp2_session_send_server(void) {
+  TEST_FAILMALLOC_RUN(run_nghttp2_session_send_server);
+}
+
 static void run_nghttp2_session_recv(void) {
   nghttp2_session *session;
   nghttp2_session_callbacks callbacks;
diff --git a/tests/failmalloc_test.h b/tests/failmalloc_test.h
index fb7e7701..c4306530 100644
--- a/tests/failmalloc_test.h
+++ b/tests/failmalloc_test.h
@@ -30,6 +30,7 @@
 #endif /* HAVE_CONFIG_H */
 
 void test_nghttp2_session_send(void);
+void test_nghttp2_session_send_server(void);
 void test_nghttp2_session_recv(void);
 void test_nghttp2_frame(void);
 void test_nghttp2_hd(void);
diff --git a/tests/main.c b/tests/main.c
index 6a985317..3aae0376 100644
--- a/tests/main.c
+++ b/tests/main.c
@@ -103,6 +103,8 @@ int main(int argc _U_, char *argv[] _U_) {
                    test_nghttp2_session_recv_too_large_frame_length) ||
       !CU_add_test(pSuite, "session_recv_extension",
                    test_nghttp2_session_recv_extension) ||
+      !CU_add_test(pSuite, "session_recv_altsvc",
+                   test_nghttp2_session_recv_altsvc) ||
       !CU_add_test(pSuite, "session_continue", test_nghttp2_session_continue) ||
       !CU_add_test(pSuite, "session_add_frame",
                    test_nghttp2_session_add_frame) ||
@@ -132,6 +134,8 @@ int main(int argc _U_, char *argv[] _U_) {
                    test_nghttp2_session_on_data_received) ||
       !CU_add_test(pSuite, "session_on_data_received_fail_fast",
                    test_nghttp2_session_on_data_received_fail_fast) ||
+      !CU_add_test(pSuite, "session_on_altsvc_received",
+                   test_nghttp2_session_on_altsvc_received) ||
       !CU_add_test(pSuite, "session_send_headers_start_stream",
                    test_nghttp2_session_send_headers_start_stream) ||
       !CU_add_test(pSuite, "session_send_headers_reply",
@@ -197,6 +201,7 @@ int main(int argc _U_, char *argv[] _U_) {
       !CU_add_test(pSuite, "submit_invalid_nv",
                    test_nghttp2_submit_invalid_nv) ||
       !CU_add_test(pSuite, "submit_extension", test_nghttp2_submit_extension) ||
+      !CU_add_test(pSuite, "submit_altsvc", test_nghttp2_submit_altsvc) ||
       !CU_add_test(pSuite, "session_open_stream",
                    test_nghttp2_session_open_stream) ||
       !CU_add_test(pSuite, "session_open_stream_with_idle_stream_dep",
diff --git a/tests/nghttp2_session_test.c b/tests/nghttp2_session_test.c
index 2e7dafee..b80b41b1 100644
--- a/tests/nghttp2_session_test.c
+++ b/tests/nghttp2_session_test.c
@@ -1955,6 +1955,124 @@ void test_nghttp2_session_recv_extension(void) {
   nghttp2_option_del(option);
 }
 
+void test_nghttp2_session_recv_altsvc(void) {
+  nghttp2_session *session;
+  nghttp2_session_callbacks callbacks;
+  my_user_data ud;
+  nghttp2_buf buf;
+  nghttp2_frame_hd hd;
+  nghttp2_mem *mem;
+  ssize_t rv;
+  nghttp2_option *option;
+  static const uint8_t origin[] = "nghttp2.org";
+  static const uint8_t field_value[] = "h2=\":443\"";
+
+  mem = nghttp2_mem_default();
+
+  nghttp2_buf_init2(&buf, NGHTTP2_FRAME_HDLEN + NGHTTP2_MAX_FRAME_SIZE_MIN,
+                    mem);
+
+  memset(&callbacks, 0, sizeof(nghttp2_session_callbacks));
+
+  callbacks.on_frame_recv_callback = on_frame_recv_callback;
+
+  nghttp2_option_new(&option);
+  nghttp2_option_set_builtin_recv_extension_type(option, NGHTTP2_ALTSVC);
+
+  nghttp2_session_client_new2(&session, &callbacks, &ud, option);
+
+  nghttp2_frame_hd_init(&hd, 2 + sizeof(origin) - 1 + sizeof(field_value) - 1,
+                        NGHTTP2_ALTSVC, NGHTTP2_FLAG_NONE, 0);
+  nghttp2_frame_pack_frame_hd(buf.last, &hd);
+  buf.last += NGHTTP2_FRAME_HDLEN;
+  nghttp2_put_uint16be(buf.last, sizeof(origin) - 1);
+  buf.last += 2;
+  buf.last = nghttp2_cpymem(buf.last, origin, sizeof(origin) - 1);
+  buf.last = nghttp2_cpymem(buf.last, field_value, sizeof(field_value) - 1);
+
+  ud.frame_recv_cb_called = 0;
+  rv = nghttp2_session_mem_recv(session, buf.pos, nghttp2_buf_len(&buf));
+
+  CU_ASSERT((ssize_t)nghttp2_buf_len(&buf) == rv);
+  CU_ASSERT(1 == ud.frame_recv_cb_called);
+  CU_ASSERT(NGHTTP2_ALTSVC == ud.recv_frame_hd.type);
+  CU_ASSERT(NGHTTP2_FLAG_NONE == ud.recv_frame_hd.flags);
+  CU_ASSERT(0 == ud.recv_frame_hd.stream_id);
+
+  nghttp2_session_del(session);
+
+  /* size of origin is larger than frame length */
+  nghttp2_buf_reset(&buf);
+
+  nghttp2_session_client_new2(&session, &callbacks, &ud, option);
+
+  nghttp2_frame_hd_init(&hd, 2 + sizeof(origin) - 1 - 1, NGHTTP2_ALTSVC,
+                        NGHTTP2_FLAG_NONE, 0);
+  nghttp2_frame_pack_frame_hd(buf.last, &hd);
+  buf.last += NGHTTP2_FRAME_HDLEN;
+  nghttp2_put_uint16be(buf.last, sizeof(origin) - 1);
+  buf.last += 2;
+  buf.last = nghttp2_cpymem(buf.last, origin, sizeof(origin) - 1 - 1);
+
+  ud.frame_recv_cb_called = 0;
+  rv = nghttp2_session_mem_recv(session, buf.pos, nghttp2_buf_len(&buf));
+
+  CU_ASSERT((ssize_t)nghttp2_buf_len(&buf) == rv);
+  CU_ASSERT(0 == ud.frame_recv_cb_called);
+
+  nghttp2_session_del(session);
+
+  /* send large frame (16KiB) */
+  nghttp2_buf_reset(&buf);
+
+  nghttp2_session_client_new2(&session, &callbacks, &ud, option);
+
+  nghttp2_frame_hd_init(&hd, NGHTTP2_MAX_FRAME_SIZE_MIN, NGHTTP2_ALTSVC,
+                        NGHTTP2_FLAG_NONE, 0);
+  nghttp2_frame_pack_frame_hd(buf.last, &hd);
+  buf.last += NGHTTP2_FRAME_HDLEN;
+  nghttp2_put_uint16be(buf.last, sizeof(origin) - 1);
+  buf.last += 2;
+  buf.last = nghttp2_cpymem(buf.last, origin, sizeof(origin) - 1);
+  memset(buf.last, 0, nghttp2_buf_avail(&buf));
+  buf.last += nghttp2_buf_avail(&buf);
+
+  ud.frame_recv_cb_called = 0;
+  rv = nghttp2_session_mem_recv(session, buf.pos, nghttp2_buf_len(&buf));
+
+  CU_ASSERT((ssize_t)nghttp2_buf_len(&buf) == rv);
+  CU_ASSERT(1 == ud.frame_recv_cb_called);
+  CU_ASSERT(NGHTTP2_ALTSVC == ud.recv_frame_hd.type);
+  CU_ASSERT(NGHTTP2_MAX_FRAME_SIZE_MIN == ud.recv_frame_hd.length);
+
+  nghttp2_session_del(session);
+
+  /* received by server */
+  nghttp2_buf_reset(&buf);
+
+  nghttp2_session_server_new2(&session, &callbacks, &ud, option);
+
+  nghttp2_frame_hd_init(&hd, 2 + sizeof(origin) - 1 + sizeof(field_value) - 1,
+                        NGHTTP2_ALTSVC, NGHTTP2_FLAG_NONE, 0);
+  nghttp2_frame_pack_frame_hd(buf.last, &hd);
+  buf.last += NGHTTP2_FRAME_HDLEN;
+  nghttp2_put_uint16be(buf.last, sizeof(origin) - 1);
+  buf.last += 2;
+  buf.last = nghttp2_cpymem(buf.last, origin, sizeof(origin) - 1);
+  buf.last = nghttp2_cpymem(buf.last, field_value, sizeof(field_value) - 1);
+
+  ud.frame_recv_cb_called = 0;
+  rv = nghttp2_session_mem_recv(session, buf.pos, nghttp2_buf_len(&buf));
+
+  CU_ASSERT((ssize_t)nghttp2_buf_len(&buf) == rv);
+  CU_ASSERT(0 == ud.frame_recv_cb_called);
+
+  nghttp2_session_del(session);
+
+  nghttp2_buf_free(&buf, mem);
+  nghttp2_option_del(option);
+}
+
 void test_nghttp2_session_continue(void) {
   nghttp2_session *session;
   nghttp2_session_callbacks callbacks;
@@ -3364,6 +3482,113 @@ void test_nghttp2_session_on_data_received_fail_fast(void) {
   nghttp2_session_del(session);
 }
 
+void test_nghttp2_session_on_altsvc_received(void) {
+  nghttp2_session *session;
+  nghttp2_session_callbacks callbacks;
+  my_user_data ud;
+  nghttp2_frame frame;
+  nghttp2_mem *mem;
+  nghttp2_option *option;
+  uint8_t origin[] = "nghttp2.org";
+  uint8_t field_value[] = "h2=\":443\"";
+  int rv;
+
+  mem = nghttp2_mem_default();
+
+  memset(&callbacks, 0, sizeof(nghttp2_session_callbacks));
+  callbacks.on_frame_recv_callback = on_frame_recv_callback;
+
+  nghttp2_option_new(&option);
+  nghttp2_option_set_builtin_recv_extension_type(option, NGHTTP2_ALTSVC);
+
+  nghttp2_session_client_new2(&session, &callbacks, &ud, option);
+
+  frame.ext.payload = &session->iframe.ext_frame_payload;
+
+  /* We just pass the strings without making a copy.  This is OK,
+     since we never call nghttp2_frame_altsvc_free(). */
+  nghttp2_frame_altsvc_init(&frame.ext, 0, origin, sizeof(origin) - 1,
+                            field_value, sizeof(field_value) - 1);
+
+  ud.frame_recv_cb_called = 0;
+  rv = nghttp2_session_on_altsvc_received(session, &frame);
+
+  CU_ASSERT(0 == rv);
+  CU_ASSERT(1 == ud.frame_recv_cb_called);
+
+  nghttp2_session_del(session);
+
+  /* Receiving empty origin with stream ID == 0 */
+  nghttp2_session_client_new2(&session, &callbacks, &ud, option);
+
+  frame.ext.payload = &session->iframe.ext_frame_payload;
+
+  nghttp2_frame_altsvc_init(&frame.ext, 0, origin, 0, field_value,
+                            sizeof(field_value) - 1);
+
+  ud.frame_recv_cb_called = 0;
+  rv = nghttp2_session_on_altsvc_received(session, &frame);
+
+  CU_ASSERT(0 == rv);
+  CU_ASSERT(0 == ud.frame_recv_cb_called);
+
+  nghttp2_session_del(session);
+
+  /* Receiving non-empty origin with stream ID != 0 */
+  nghttp2_session_client_new2(&session, &callbacks, &ud, option);
+
+  frame.ext.payload = &session->iframe.ext_frame_payload;
+
+  open_sent_stream(session, 1);
+
+  nghttp2_frame_altsvc_init(&frame.ext, 1, origin, sizeof(origin) - 1,
+                            field_value, sizeof(field_value) - 1);
+
+  ud.frame_recv_cb_called = 0;
+  rv = nghttp2_session_on_altsvc_received(session, &frame);
+
+  CU_ASSERT(0 == rv);
+  CU_ASSERT(0 == ud.frame_recv_cb_called);
+
+  nghttp2_session_del(session);
+
+  /* Receiving empty origin with stream ID != 0; this is OK */
+  nghttp2_session_client_new2(&session, &callbacks, &ud, option);
+
+  frame.ext.payload = &session->iframe.ext_frame_payload;
+
+  open_sent_stream(session, 1);
+
+  nghttp2_frame_altsvc_init(&frame.ext, 1, origin, 0, field_value,
+                            sizeof(field_value) - 1);
+
+  ud.frame_recv_cb_called = 0;
+  rv = nghttp2_session_on_altsvc_received(session, &frame);
+
+  CU_ASSERT(0 == rv);
+  CU_ASSERT(1 == ud.frame_recv_cb_called);
+
+  nghttp2_session_del(session);
+
+  /* Stream does not exist; ALTSVC will be ignored. */
+  nghttp2_session_client_new2(&session, &callbacks, &ud, option);
+
+  frame.ext.payload = &session->iframe.ext_frame_payload;
+
+  nghttp2_frame_altsvc_init(&frame.ext, 1, origin, 0, field_value,
+                            sizeof(field_value) - 1);
+
+  ud.frame_recv_cb_called = 0;
+  rv = nghttp2_session_on_altsvc_received(session, &frame);
+
+  CU_ASSERT(0 == rv);
+  CU_ASSERT(0 == ud.frame_recv_cb_called);
+
+  nghttp2_session_del(session);
+
+  nghttp2_option_del(option);
+}
+
 void test_nghttp2_session_send_headers_start_stream(void) {
   nghttp2_session *session;
   nghttp2_session_callbacks callbacks;
@@ -5217,6 +5442,82 @@ void test_nghttp2_submit_extension(void) {
   nghttp2_buf_free(&ud.scratchbuf, mem);
 }
 
+void test_nghttp2_submit_altsvc(void) {
+  nghttp2_session *session;
+  nghttp2_session_callbacks callbacks;
+  nghttp2_mem *mem;
+  my_user_data ud;
+  int rv;
+  ssize_t len;
+  const uint8_t *data;
+  nghttp2_frame_hd hd;
+  size_t origin_len;
+
+  mem = nghttp2_mem_default();
+
+  memset(&callbacks, 0, sizeof(nghttp2_session_callbacks));
+
+  nghttp2_session_server_new(&session, &callbacks, &ud);
+
+  const uint8_t origin[] = "nghttp2.org";
+  const uint8_t field_value[] = "h2=\":443\"";
+
+  rv = nghttp2_submit_altsvc(session, NGHTTP2_FLAG_NONE, 0, origin,
+                             sizeof(origin) - 1, field_value,
+                             sizeof(field_value) - 1);
+
+  CU_ASSERT(0 == rv);
+
+  ud.frame_send_cb_called = 0;
+
+  len = nghttp2_session_mem_send(session, &data);
+
+  CU_ASSERT(len ==
+            NGHTTP2_FRAME_HDLEN + 2 + sizeof(origin) - 1 + sizeof(field_value) -
+                1);
+
+  nghttp2_frame_unpack_frame_hd(&hd, data);
+
+  CU_ASSERT(2 + sizeof(origin) - 1 + sizeof(field_value) - 1 == hd.length);
+  CU_ASSERT(NGHTTP2_ALTSVC == hd.type);
+  CU_ASSERT(NGHTTP2_FLAG_NONE == hd.flags);
+
+  origin_len = nghttp2_get_uint16(data + NGHTTP2_FRAME_HDLEN);
+
+  CU_ASSERT(sizeof(origin) - 1 == origin_len);
+  CU_ASSERT(0 ==
+            memcmp(origin, data + NGHTTP2_FRAME_HDLEN + 2, sizeof(origin) - 1));
+  CU_ASSERT(0 == memcmp(field_value,
+                        data + NGHTTP2_FRAME_HDLEN + 2 + sizeof(origin) - 1,
+                        hd.length - (sizeof(origin) - 1) - 2));
+
+  /* submitting empty origin with stream_id == 0 is error */
+  rv = nghttp2_submit_altsvc(session, NGHTTP2_FLAG_NONE, 0, NULL, 0,
+                             field_value, sizeof(field_value) - 1);
+
+  CU_ASSERT(NGHTTP2_ERR_INVALID_ARGUMENT == rv);
+
+  /* submitting non-empty origin with stream_id != 0 is error */
+  rv = nghttp2_submit_altsvc(session, NGHTTP2_FLAG_NONE, 1, origin,
+                             sizeof(origin) - 1, field_value,
+                             sizeof(field_value) - 1);
+
+  CU_ASSERT(NGHTTP2_ERR_INVALID_ARGUMENT == rv);
+
+  nghttp2_session_del(session);
+
+  /* submitting from client side session is error */
+  nghttp2_session_client_new(&session, &callbacks, NULL);
+
+  rv = nghttp2_submit_altsvc(session, NGHTTP2_FLAG_NONE, 0, origin,
+                             sizeof(origin) - 1, field_value,
+                             sizeof(field_value) - 1);
+
+  CU_ASSERT(NGHTTP2_ERR_INVALID_STATE == rv);
+
+  nghttp2_session_del(session);
+}
+
 void test_nghttp2_session_open_stream(void) {
   nghttp2_session *session;
   nghttp2_session_callbacks callbacks;
diff --git a/tests/nghttp2_session_test.h b/tests/nghttp2_session_test.h
index 27415c2f..3787b6e4 100644
--- a/tests/nghttp2_session_test.h
+++ b/tests/nghttp2_session_test.h
@@ -45,6 +45,7 @@ void test_nghttp2_session_recv_unexpected_continuation(void);
 void test_nghttp2_session_recv_settings_header_table_size(void);
 void test_nghttp2_session_recv_too_large_frame_length(void);
 void test_nghttp2_session_recv_extension(void);
+void test_nghttp2_session_recv_altsvc(void);
 void test_nghttp2_session_continue(void);
 void test_nghttp2_session_add_frame(void);
 void test_nghttp2_session_on_request_headers_received(void);
@@ -60,6 +61,7 @@ void test_nghttp2_session_on_goaway_received(void);
 void test_nghttp2_session_on_window_update_received(void);
 void test_nghttp2_session_on_data_received(void);
 void test_nghttp2_session_on_data_received_fail_fast(void);
+void test_nghttp2_session_on_altsvc_received(void);
 void test_nghttp2_session_send_headers_start_stream(void);
 void test_nghttp2_session_send_headers_reply(void);
 void test_nghttp2_session_send_headers_frame_size_error(void);
@@ -95,6 +97,7 @@ void test_nghttp2_submit_window_update_local_window_size(void);
 void test_nghttp2_submit_shutdown_notice(void);
 void test_nghttp2_submit_invalid_nv(void);
 void test_nghttp2_submit_extension(void);
+void test_nghttp2_submit_altsvc(void);
 void test_nghttp2_session_open_stream(void);
 void test_nghttp2_session_open_stream_with_idle_stream_dep(void);
 void test_nghttp2_session_get_next_ob_item(void);