diff --git a/python/sdist/amici/petab/parameter_mapping.py b/python/sdist/amici/petab/parameter_mapping.py
index 3bd0e69ac2..5bb8f2f7a8 100644
--- a/python/sdist/amici/petab/parameter_mapping.py
+++ b/python/sdist/amici/petab/parameter_mapping.py
@@ -692,6 +692,7 @@ def _subset_dict(
         Subsetted dictionary
     """
     for keys in args:
+        keys = set(keys)
         yield {key: val for (key, val) in full.items() if key in keys}