diff --git a/receive_stream.go b/receive_stream.go
index cca3f7096..f9a1e066f 100644
--- a/receive_stream.go
+++ b/receive_stream.go
@@ -166,13 +166,10 @@ func (s *receiveStream) readImpl(p []byte) (bool /*stream completed */, int, err
 			return false, bytesRead, fmt.Errorf("BUG: readPosInFrame (%d) > frame.DataLen (%d) in stream.Read", s.readPosInFrame, len(s.currentFrame))
 		}
 
-		s.mutex.Unlock()
-
 		m := copy(p[bytesRead:], s.currentFrame[s.readPosInFrame:])
 		s.readPosInFrame += m
 		bytesRead += m
 
-		s.mutex.Lock()
 		// when a RESET_STREAM was received, the was already informed about the final byteOffset for this stream
 		if !s.resetRemotely {
 			s.flowController.AddBytesRead(protocol.ByteCount(m))