diff --git a/python/dumux/common/properties.py b/python/dumux/common/properties.py
index 5f2fc18e842d6a278d61bec3e69a638955fcc900..e72dc23f05a089a4c44c2a4fd62f0ab2ca22f696 100644
--- a/python/dumux/common/properties.py
+++ b/python/dumux/common/properties.py
@@ -173,7 +173,7 @@ class TypeTag:
         self.gridGeometry = gridGeometry
         self.name = name
 
-        if self.name in _typeTags.keys():
+        if self.name in _typeTags:
             if inheritsFrom is not None:
                 raise ValueError(
                     f"Existing TypeTag {name} cannot inherit from other TypeTags."