diff --git a/lib/includes/nghttp2/nghttp2.h b/lib/includes/nghttp2/nghttp2.h
index 83d4173a..acfe6ecb 100644
--- a/lib/includes/nghttp2/nghttp2.h
+++ b/lib/includes/nghttp2/nghttp2.h
@@ -4136,6 +4136,36 @@ typedef struct {
   size_t field_value_len;
 } nghttp2_ext_altsvc;
 
+/**
+ * @function
+ *
+ * Submits ALTSVC frame.
+ *
+ * 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,
diff --git a/lib/nghttp2_submit.c b/lib/nghttp2_submit.c
index fc0663ce..3c6a3664 100644
--- a/lib/nghttp2_submit.c
+++ b/lib/nghttp2_submit.c
@@ -425,10 +425,22 @@ int nghttp2_submit_altsvc(nghttp2_session *session, uint8_t flags _U_,
 
   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;
@@ -437,11 +449,15 @@ int nghttp2_submit_altsvc(nghttp2_session *session, uint8_t flags _U_,
   p = buf;
 
   origin_copy = p;
-  p = nghttp2_cpymem(p, origin, origin_len);
+  if (origin_len) {
+    p = nghttp2_cpymem(p, origin, origin_len);
+  }
   *p++ = '\0';
 
   field_value_copy = p;
-  p = nghttp2_cpymem(p, field_value, field_value_len);
+  if (field_value_len) {
+    p = nghttp2_cpymem(p, field_value, field_value_len);
+  }
   *p++ = '\0';
 
   item = nghttp2_mem_malloc(mem, sizeof(nghttp2_outbound_item));
@@ -470,6 +486,8 @@ int nghttp2_submit_altsvc(nghttp2_session *session, uint8_t flags _U_,
   if (rv != 0) {
     nghttp2_frame_altsvc_free(&frame->ext, mem);
     nghttp2_mem_free(mem, item);
+
+    return rv;
   }
 
   return 0;