diff --git a/src/calibre/srv/web_socket.py b/src/calibre/srv/web_socket.py
index 7314e31a81..d37ccba535 100644
--- a/src/calibre/srv/web_socket.py
+++ b/src/calibre/srv/web_socket.py
@@ -320,7 +320,7 @@ class WebSocketConnection(HTTPConnection):
                 self.websocket_close(PROTOCOL_ERROR, 'Continuation frame without any message to continue')
                 return
             self.current_recv_opcode = opcode
-        elif opcode != CONTINUATION:
+        elif frame_starting and opcode != CONTINUATION:
             self.log.error('Client sent continuation frame with non-zero opcode')
             self.websocket_close(PROTOCOL_ERROR, 'Continuation frame with non-zero opcode')
             return