diff --git a/aiogremlin/connection.py b/aiogremlin/connection.py
index 7f265d1aa7a336e236a2a653a7e6d5df614d2555..95ab5928491343faa9823d46dcdd2be2da6d957d 100644
--- a/aiogremlin/connection.py
+++ b/aiogremlin/connection.py
@@ -231,6 +231,8 @@ class GremlinClientWebSocketResponse(BaseConnection, ClientWebSocketResponse):
                             self.parser.feed_data(msg.data.decode())
                         elif msg.tp == MsgType.text:
                             self.parser.feed_data(msg.data.strip())
+                        else:
+                            raise RuntimeError("Unknown message type.")
                         break
         finally:
             self._waiting = False