diff --git a/app/skeleton.py b/app/skeleton.py
index b1aabd3..b6e871a 100644
--- a/app/skeleton.py
+++ b/app/skeleton.py
@@ -93,9 +93,10 @@ def merge_with_skeleton(data: Dict, skel: Dict) -> Dict:
         * Split info less complex functions
     """
     # First, check for illegal keys
-    for key in data:
-        if key not in skel:
-            raise InvalidKeyError(key)
+    key = next(key not in skel for key in data)
+
+    if key:
+        raise InvalidKeyError(key)
 
     # Then, check the default values
     for key, value in skel.items():