diff --git a/pysr/sr.py b/pysr/sr.py
index 41ee8e905..a9861ef33 100644
--- a/pysr/sr.py
+++ b/pysr/sr.py
@@ -1732,8 +1732,10 @@ def _run(self, X, y, mutated_params, weights, seed):
             jl_y,
             weights=jl_weights,
             niterations=int(self.niterations),
-            variable_names=jl_array(self.feature_names_in_.tolist()),
-            display_variable_names=jl_array(self.display_feature_names_in_.tolist()),
+            variable_names=jl_array([str(v) for v in self.feature_names_in_]),
+            display_variable_names=jl_array(
+                [str(v) for v in self.display_feature_names_in_]
+            ),
             y_variable_names=jl_y_variable_names,
             X_units=jl_array(self.X_units_),
             y_units=jl_array(self.y_units_),