diff --git a/revpi-server.py b/revpi-server.py
index 0c62e58..2467b76 100644
--- a/revpi-server.py
+++ b/revpi-server.py
@@ -327,7 +327,7 @@ async def get_client_requests(self, client, path):
 
                 if command == "login":
                     client_version = str(args[0])
-                    if client_version in self.supported_client_versions:
+                    if not client_version in self.supported_client_versions:
                         logging.info("Unsupported client version")
                         return_message = {"error": "ERROR_UNSUPPORTED_VERSION"}
                         self.send_websocket_message(client, message + ";" + json.dumps(return_message))