diff --git a/lib/nghttp2_http.c b/lib/nghttp2_http.c
index 115b4007..1f4cfa8b 100644
--- a/lib/nghttp2_http.c
+++ b/lib/nghttp2_http.c
@@ -382,15 +382,33 @@ static int http_response_on_header(nghttp2_stream *stream, nghttp2_nv *nv,
 
 int nghttp2_http_on_header(nghttp2_session *session, nghttp2_stream *stream,
                            nghttp2_frame *frame, nghttp2_nv *nv, int trailer) {
-  if (!nghttp2_check_header_name(nv->name, nv->namelen) ||
-      !nghttp2_check_header_value(nv->value, nv->valuelen)) {
-    /* We are strict for pseudo header field.  One bad character
-       should lead to fail.  OTOH, we should be a bit forgiving for
-       regular headers, since existing public internet has so much
-       illegal headers floating around and if we kill the stream
-       because of this, we may disrupt many web sites and/or
-       libraries.  So we become conservative here, and just ignore
-       those illegal regular headers. */
+  /* We are strict for pseudo header field.  One bad character should
+     lead to fail.  OTOH, we should be a bit forgiving for regular
+     headers, since existing public internet has so much illegal
+     headers floating around and if we kill the stream because of
+     this, we may disrupt many web sites and/or libraries.  So we
+     become conservative here, and just ignore those illegal regular
+     headers. */
+  if (!nghttp2_check_header_name(nv->name, nv->namelen)) {
+    size_t i;
+    if (nv->namelen > 0 && nv->name[0] == ':') {
+      return -1;
+    }
+    /* header field name must be lower-cased without exception */
+    for (i = 0; i < nv->namelen; ++i) {
+      char c = nv->name[i];
+      if ('A' <= c && c <= 'Z') {
+        return -1;
+      }
+    }
+    /* When ignoring regular headers, we set this flag so that we
+       still enforce header field ordering rule for pseudo header
+       fields. */
+    stream->http_flags |= NGHTTP2_HTTP_FLAG_PSEUDO_HEADER_DISALLOWED;
+    return 1;
+  }
+
+  if (!nghttp2_check_header_value(nv->value, nv->valuelen)) {
     if (nv->namelen > 0 && nv->name[0] == ':') {
       return -1;
     }