diff --git a/qutebrowser/browser/webengine/webview.py b/qutebrowser/browser/webengine/webview.py
index 969e3c7ec..e89d01a88 100644
--- a/qutebrowser/browser/webengine/webview.py
+++ b/qutebrowser/browser/webengine/webview.py
@@ -76,7 +76,7 @@ class WebEngineView(QWebEngineView):
         if not children:
             return None
 
-        assert len(children) == 1
+        assert len(children) == 1, children
         return children[0]
 
     def shutdown(self):