diff --git a/python/sdist/amici/numpy.py b/python/sdist/amici/numpy.py
index 97cb624f4a..487e5d7b98 100644
--- a/python/sdist/amici/numpy.py
+++ b/python/sdist/amici/numpy.py
@@ -93,7 +93,7 @@ def __init__(self, swigptr):
 
         # create properties for all fields
         for field in self._field_names:
-            if not hasattr(self, field):
+            if field not in dir(self):
                 setattr(
                     self,
                     field,