diff --git a/python/mujoco/experimental/studio/sim.cc b/python/mujoco/experimental/studio/sim.cc
index e77efbfc..1a6906b5 100644
--- a/python/mujoco/experimental/studio/sim.cc
+++ b/python/mujoco/experimental/studio/sim.cc
@@ -43,22 +43,13 @@ PYBIND11_MODULE(sim, m) {
       .def(py::init<>())
       .def(
           "advance",
-          [](StepControl& self, py::object model_obj, py::object data_obj,
-             py::object step_fn) {
+          [](StepControl& self, py::object model_obj, py::object data_obj) {
             auto& model = py::cast<mujoco::python::MjModelWrapper&>(model_obj);
             auto& data = py::cast<mujoco::python::MjDataWrapper&>(data_obj);
-            if (step_fn.is_none()) {
-              py::gil_scoped_release no_gil;
-              return self.Advance(model.get(), data.get());
-            } else {
-              return self.Advance(
-                  model.get(), data.get(),
-                  [step_fn, model_obj, data_obj](mjModel*, mjData*) {
-                    step_fn(model_obj, data_obj);
-                  });
-            }
+            py::gil_scoped_release no_gil;
+            return self.Advance(model.get(), data.get());
           },
-          py::arg("model"), py::arg("data"), py::arg("step_fn") = py::none(),
+          py::arg("model"), py::arg("data"),
           "Step physics forward, respecting speed settings and refresh budget.")
       .def("force_sync", &StepControl::ForceSync,
            "Ensures the next Advance() will synchronize time and step once.")
diff --git a/src/experimental/platform/sim/step_control.cc b/src/experimental/platform/sim/step_control.cc
index 88d33f18..7f0122da 100644
--- a/src/experimental/platform/sim/step_control.cc
+++ b/src/experimental/platform/sim/step_control.cc
@@ -92,8 +92,7 @@ StepControl::PauseState StepControl::GetPauseState() const {
   return pause_state_;
 }
 
-StepControl::Status StepControl::Advance(mjModel* m, mjData* d,
-                                         StepFn step_fn) {
+StepControl::Status StepControl::Advance(mjModel* m, mjData* d) {
   if (!m) {
     return Status::kOk;
   }
@@ -187,11 +186,7 @@ StepControl::Status StepControl::Advance(mjModel* m, mjData* d,
     if (pre_step_) {
       pre_step_(m, d);
     }
-    if (step_fn) {
-      step_fn(m, d);
-    } else {
-      mj_step(m, d);
-    }
+    mj_step(m, d);
     if (post_step_) {
       post_step_(m, d);
     }
diff --git a/src/experimental/platform/sim/step_control.h b/src/experimental/platform/sim/step_control.h
index b3bd5b2f..cafe7cb1 100644
--- a/src/experimental/platform/sim/step_control.h
+++ b/src/experimental/platform/sim/step_control.h
@@ -55,7 +55,7 @@ class StepControl {
       mjWARN_BADQACC, mjWARN_BADQVEL, mjWARN_BADQPOS};
 
   // Steps physics forward, respecting speed settings and refresh budget.
-  Status Advance(mjModel* m, mjData* d, StepFn step_fn = nullptr);
+  Status Advance(mjModel* m, mjData* d);
 
   // Ensures the next call to Advance() will synchronize time and step once.
   void ForceSync();