diff --git a/lib/nghttp2_http.c b/lib/nghttp2_http.c
index 8240f8d7..b08f8863 100644
--- a/lib/nghttp2_http.c
+++ b/lib/nghttp2_http.c
@@ -244,7 +244,7 @@ static int http_response_on_header(nghttp2_stream *stream, nghttp2_hd_nv *nv,
       return NGHTTP2_ERR_HTTP_HEADER;
     }
     stream->status_code = (int16_t)parse_uint(nv->value->base, nv->value->len);
-    if (stream->status_code == -1) {
+    if (stream->status_code == -1 || stream->status_code == 101) {
       return NGHTTP2_ERR_HTTP_HEADER;
     }
     break;
diff --git a/tests/nghttp2_session_test.c b/tests/nghttp2_session_test.c
index f2756aad..2089dbbf 100644
--- a/tests/nghttp2_session_test.c
+++ b/tests/nghttp2_session_test.c
@@ -10437,6 +10437,7 @@ void test_nghttp2_http_mandatory_headers(void) {
                                     MAKE_NV("content-length", "0")};
   const nghttp2_nv clnonzero204_resnv[] = {MAKE_NV(":status", "204"),
                                            MAKE_NV("content-length", "100")};
+  const nghttp2_nv status101_resnv[] = {MAKE_NV(":status", "101")};
 
   /* test case for request */
   const nghttp2_nv nopath_reqnv[] = {MAKE_NV(":scheme", "https"),
@@ -10551,6 +10552,12 @@ void test_nghttp2_http_mandatory_headers(void) {
       session, &deflater, 21, NGHTTP2_STREAM_OPENING, clnonzero204_resnv,
       ARRLEN(clnonzero204_resnv));
 
+  /* status code 101 should not be used in HTTP/2 because it is used
+     for HTTP Upgrade which HTTP/2 removes. */
+  check_nghttp2_http_recv_headers_fail(session, &deflater, 23,
+                                       NGHTTP2_STREAM_OPENING, status101_resnv,
+                                       ARRLEN(status101_resnv));
+
   nghttp2_hd_deflate_free(&deflater);
 
   nghttp2_session_del(session);