diff --git a/lib/nghttp2_session.c b/lib/nghttp2_session.c
index af4bd872..d3fd30a9 100644
--- a/lib/nghttp2_session.c
+++ b/lib/nghttp2_session.c
@@ -573,6 +573,10 @@ int nghttp2_session_reprioritize_stream
   nghttp2_stream *dep_stream;
   nghttp2_stream *root_stream;
 
+  if(!nghttp2_stream_in_dep_tree(stream)) {
+    return 0;
+  }
+
   if(pri_spec->stream_id == stream->stream_id) {
     return nghttp2_session_terminate_session_with_reason
       (session, NGHTTP2_PROTOCOL_ERROR, "depend on itself");