diff --git a/zerver/lib/push_notifications.py b/zerver/lib/push_notifications.py
index ddb0de5e6d..a97748e494 100644
--- a/zerver/lib/push_notifications.py
+++ b/zerver/lib/push_notifications.py
@@ -77,6 +77,8 @@ def response_listener(error_response):
         return
 
     code = error_response['status']
+    assert isinstance(code, int)
+
     errmsg = ERROR_CODES[code]
     data = redis_client.hgetall(key)
     token = data['token']