diff --git a/lib/nghttp2_frame.c b/lib/nghttp2_frame.c
index 676a9f77..f8f73861 100644
--- a/lib/nghttp2_frame.c
+++ b/lib/nghttp2_frame.c
@@ -487,11 +487,33 @@ int nghttp2_frame_pack_rst_stream(nghttp2_bufs *bufs,
   return 0;
 }
 
+static nghttp2_error_code normalize_error_code(uint32_t error_code)
+{
+  switch(error_code) {
+  case NGHTTP2_NO_ERROR:
+  case NGHTTP2_PROTOCOL_ERROR:
+  case NGHTTP2_INTERNAL_ERROR:
+  case NGHTTP2_FLOW_CONTROL_ERROR:
+  case NGHTTP2_SETTINGS_TIMEOUT:
+  case NGHTTP2_STREAM_CLOSED:
+  case NGHTTP2_FRAME_SIZE_ERROR:
+  case NGHTTP2_REFUSED_STREAM:
+  case NGHTTP2_CANCEL:
+  case NGHTTP2_COMPRESSION_ERROR:
+  case NGHTTP2_CONNECT_ERROR:
+  case NGHTTP2_ENHANCE_YOUR_CALM:
+  case NGHTTP2_INADEQUATE_SECURITY:
+    return error_code;
+  default:
+    return NGHTTP2_INTERNAL_ERROR;
+  }
+}
+
 void nghttp2_frame_unpack_rst_stream_payload(nghttp2_rst_stream *frame,
                                              const uint8_t *payload,
                                              size_t payloadlen)
 {
-  frame->error_code = nghttp2_get_uint32(payload);
+  frame->error_code = normalize_error_code(nghttp2_get_uint32(payload));
 }
 
 int nghttp2_frame_pack_settings(nghttp2_bufs *bufs, nghttp2_settings *frame)
@@ -700,7 +722,7 @@ void nghttp2_frame_unpack_goaway_payload(nghttp2_goaway *frame,
                                          size_t var_gift_payloadlen)
 {
   frame->last_stream_id = nghttp2_get_uint32(payload) & NGHTTP2_STREAM_ID_MASK;
-  frame->error_code = nghttp2_get_uint32(payload+4);
+  frame->error_code = normalize_error_code(nghttp2_get_uint32(payload + 4));
 
   frame->opaque_data = var_gift_payload;
   frame->opaque_data_len = var_gift_payloadlen;
diff --git a/tests/nghttp2_frame_test.c b/tests/nghttp2_frame_test.c
index 5f772a34..0e96dbed 100644
--- a/tests/nghttp2_frame_test.c
+++ b/tests/nghttp2_frame_test.c
@@ -257,9 +257,26 @@ void test_nghttp2_frame_pack_rst_stream(void)
                      &oframe.hd);
   CU_ASSERT(NGHTTP2_PROTOCOL_ERROR == oframe.error_code);
 
-  nghttp2_bufs_free(&bufs);
   nghttp2_frame_rst_stream_free(&oframe);
+  nghttp2_bufs_reset(&bufs);
+
+  /* Unknown error code is treated as NGHTTP2_INTERNAL_ERROR */
+  frame.error_code = 1000000009;
+  rv = nghttp2_frame_pack_rst_stream(&bufs, &frame);
+
+  CU_ASSERT(0 == rv);
+  CU_ASSERT(0 == unpack_framebuf((nghttp2_frame*)&oframe, &bufs));
+
+  check_frame_header(4, NGHTTP2_RST_STREAM, NGHTTP2_FLAG_NONE, 1000000007,
+                     &oframe.hd);
+
+  CU_ASSERT(NGHTTP2_INTERNAL_ERROR == oframe.error_code);
+
+  nghttp2_frame_rst_stream_free(&oframe);
+
   nghttp2_frame_rst_stream_free(&frame);
+
+  nghttp2_bufs_free(&bufs);
 }
 
 void test_nghttp2_frame_pack_settings()
@@ -403,9 +420,24 @@ void test_nghttp2_frame_pack_goaway()
   CU_ASSERT(opaque_data_len == oframe.opaque_data_len);
   CU_ASSERT(memcmp(opaque_data, oframe.opaque_data, opaque_data_len) == 0);
 
-  nghttp2_bufs_free(&bufs);
   nghttp2_frame_goaway_free(&oframe);
+  nghttp2_bufs_reset(&bufs);
+
+  /* Unknown error code is treated as NGHTTP2_INTERNAL_ERROR */
+  frame.error_code = 1000000009;
+
+  rv = nghttp2_frame_pack_goaway(&bufs, &frame);
+
+  CU_ASSERT(0 == rv);
+  CU_ASSERT(0 == unpack_framebuf((nghttp2_frame*)&oframe, &bufs));
+  check_frame_header(24, NGHTTP2_GOAWAY, NGHTTP2_FLAG_NONE, 0, &oframe.hd);
+  CU_ASSERT(NGHTTP2_INTERNAL_ERROR == oframe.error_code);
+
+  nghttp2_frame_goaway_free(&oframe);
+
   nghttp2_frame_goaway_free(&frame);
+
+  nghttp2_bufs_free(&bufs);
 }
 
 void test_nghttp2_frame_pack_window_update(void)