diff --git a/python/sdist/amici/petab/conditions.py b/python/sdist/amici/petab/conditions.py
index ab06e8850d..2d72858580 100644
--- a/python/sdist/amici/petab/conditions.py
+++ b/python/sdist/amici/petab/conditions.py
@@ -156,8 +156,9 @@ def _get_par(model_par, value, mapping):
         key: _get_par(key, val, map_sim_fix)
         for key, val in map_sim_fix.items()
     }
+    map_sim_fix_var = map_sim_fix | map_sim_var
     map_sim_var = {
-        key: _get_par(key, val, dict(map_sim_fix, **map_sim_var))
+        key: _get_par(key, val, map_sim_fix_var)
         for key, val in map_sim_var.items()
     }