diff --git a/examples/spdycat.cc b/examples/spdycat.cc
index ac8718f0..f0512fdb 100644
--- a/examples/spdycat.cc
+++ b/examples/spdycat.cc
@@ -350,6 +350,7 @@ int run(char **uris, int n)
     callbacks.on_ctrl_send_callback = on_ctrl_send_callback3;
     callbacks.on_ctrl_recv_parse_error_callback =
       on_ctrl_recv_parse_error_callback;
+    callbacks.on_unknown_ctrl_recv_callback = on_unknown_ctrl_recv_callback;
   } else {
     callbacks.on_ctrl_recv_callback = on_ctrl_recv_callback2;
     callbacks.on_ctrl_send_callback = on_ctrl_send_callback2;
diff --git a/examples/spdylay_ssl.cc b/examples/spdylay_ssl.cc
index fe5ad23d..56a57215 100644
--- a/examples/spdylay_ssl.cc
+++ b/examples/spdylay_ssl.cc
@@ -414,6 +414,19 @@ const char* spdylay_strerror(int error_code)
 };
 } // namespace
 
+namespace {
+void dump_header(const uint8_t *head, size_t headlen)
+{
+  size_t i;
+  print_frame_attr_indent();
+  printf("Header dump: ");
+  for(i = 0; i < headlen; ++i) {
+    printf("%02X ", head[i]);
+  }
+  printf("\n");
+}
+} // namespace
+
 void on_ctrl_recv_parse_error_callback(spdylay_session *session,
                                        spdylay_frame_type type,
                                        const uint8_t *head,
@@ -422,16 +435,23 @@ void on_ctrl_recv_parse_error_callback(spdylay_session *session,
                                        size_t payloadlen,
                                        int error_code, void *user_data)
 {
-  size_t i;
   print_timer();
   printf(" recv %s frame: Parse error [%s]\n", ctrl_names[type-1],
          spdylay_strerror(error_code));
-  print_frame_attr_indent();
-  printf("Header dump: ");
-  for(i = 0; i < headlen; ++i) {
-    printf("%02X ", head[i]);
-  }
-  printf("\n");
+  dump_header(head, headlen);
+  fflush(stdout);
+}
+
+void on_unknown_ctrl_recv_callback(spdylay_session *session,
+                                   const uint8_t *head,
+                                   size_t headlen,
+                                   const uint8_t *payload,
+                                   size_t payloadlen,
+                                   void *user_data)
+{
+  print_timer();
+  printf(" recv unknown frame\n");
+  dump_header(head, headlen);
   fflush(stdout);
 }
 
diff --git a/examples/spdylay_ssl.h b/examples/spdylay_ssl.h
index 00664c58..e37ff0d4 100644
--- a/examples/spdylay_ssl.h
+++ b/examples/spdylay_ssl.h
@@ -93,6 +93,13 @@ void on_ctrl_recv_parse_error_callback(spdylay_session *session,
                                        size_t payloadlen,
                                        int error_code, void *user_data);
 
+void on_unknown_ctrl_recv_callback(spdylay_session *session,
+                                   const uint8_t *head,
+                                   size_t headlen,
+                                   const uint8_t *payload,
+                                   size_t payloadlen,
+                                   void *user_data);
+
 void on_ctrl_send_callback
 (spdylay_session *session, spdylay_frame_type type, spdylay_frame *frame,
  void *user_data);
diff --git a/lib/includes/spdylay/spdylay.h b/lib/includes/spdylay/spdylay.h
index 8ef664ed..a5b2967d 100644
--- a/lib/includes/spdylay/spdylay.h
+++ b/lib/includes/spdylay/spdylay.h
@@ -978,6 +978,24 @@ typedef void (*spdylay_on_ctrl_recv_parse_error_callback)
  const uint8_t *payload, size_t payloadlen,
  int error_code, void *user_data);
 
+/**
+ * @functypedef
+ *
+ * Callback function invoked when the received control frame type is
+ * unknown. The |head| is the pointer to the header of the received
+ * frame. The |headlen| is the length of the |head|. According to the
+ * SPDY spec, the |headlen| is always 8. In other words, the |head| is
+ * the first 8 bytes of the received frame.  The |payload| is the
+ * pointer to the data portion of the received frame.  The
+ * |payloadlen| is the length of the |payload|. This is the data after
+ * the length field.
+ */
+typedef void (*spdylay_on_unknown_ctrl_recv_callback)
+(spdylay_session *session,
+ const uint8_t *head, size_t headlen,
+ const uint8_t *payload, size_t payloadlen,
+ void *user_data);
+
 #define SPDYLAY_MAX_SCHEME 255
 #define SPDYLAY_MAX_HOSTNAME 255
 
@@ -1143,6 +1161,11 @@ typedef struct {
    * could not be parsed correctly.
    */
   spdylay_on_ctrl_recv_parse_error_callback on_ctrl_recv_parse_error_callback;
+  /**
+   * Callback function invoked when the received control frame type is
+   * unknown.
+   */
+  spdylay_on_unknown_ctrl_recv_callback on_unknown_ctrl_recv_callback;
 } spdylay_session_callbacks;
 
 /**
@@ -1404,6 +1427,9 @@ int spdylay_session_send(spdylay_session *session);
  *   3.4. If the received frame could not be unpacked correctly,
  *        :member:`spdylay_session_callbacks.on_ctrl_recv_parse_error_callback`
  *        is invoked.
+ *   3.5. If the received frame type is unknown,
+ *        :member:`spdylay_session_callbacks.on_unknown_ctrl_recv_callback`
+ *        is invoked.
  *
  * This function returns 0 if it succeeds, or one of the following
  * negative error codes:
diff --git a/lib/spdylay_session.c b/lib/spdylay_session.c
index e1fdc175..7811c78b 100644
--- a/lib/spdylay_session.c
+++ b/lib/spdylay_session.c
@@ -2199,6 +2199,17 @@ static int spdylay_session_process_ctrl_frame(spdylay_session *session)
       r = spdylay_session_fail_session(session, SPDYLAY_GOAWAY_PROTOCOL_ERROR);
     }
     break;
+  default:
+    /* Unknown frame */
+    if(session->callbacks.on_unknown_ctrl_recv_callback) {
+      session->callbacks.on_unknown_ctrl_recv_callback
+        (session,
+         session->iframe.headbuf,
+         sizeof(session->iframe.headbuf),
+         session->iframe.buf,
+         session->iframe.len,
+         session->user_data);
+    }
   }
   if(spdylay_is_fatal(r)) {
     return r;