diff --git a/python/mujoco/simulate.cc b/python/mujoco/simulate.cc
index 56fe44371d..decdbf3d5e 100644
--- a/python/mujoco/simulate.cc
+++ b/python/mujoco/simulate.cc
@@ -277,8 +277,10 @@ PYBIND11_MODULE(_simulate, pymodule) {
       .def_property_readonly("busywait",
                              GetIfNotNull(&mujoco::Simulate::busywait),
                              py::call_guard<py::gil_scoped_release>())
-      .def_property_readonly("run", GetIfNotNull(&mujoco::Simulate::run),
-                             py::call_guard<py::gil_scoped_release>())
+      .def_property("run",
+                    GetIfNotNull(&mujoco::Simulate::run),
+                    SetIfNotNull(&mujoco::Simulate::run),
+                    py::call_guard<py::gil_scoped_release>())
 
       .def_property_readonly("exitrequest",
                              CallIfNotNull(+[](mujoco::Simulate& sim) {
diff --git a/python/mujoco/viewer.py b/python/mujoco/viewer.py
index 65852c877f..f5a8dfbd09 100644
--- a/python/mujoco/viewer.py
+++ b/python/mujoco/viewer.py
@@ -115,6 +115,21 @@ def viewport(self):
       return sim.viewport
     return None
 
+  @property
+  def run(self):
+    sim = self._sim()
+    if sim is not None:
+      return sim.run
+    return None
+
+  @run.setter
+  def run(self, value):
+    if value != 0 and value != 1:
+      raise ValueError('run must be 0 or 1')
+    sim = self._sim()
+    with sim.lock():
+      sim.run = value
+
   def set_figures(self, viewports_figures):
     sim = self._sim()
     if sim is not None:
diff --git a/simulate/simulate.cc b/simulate/simulate.cc
index bf4b4a13ef..9e9c3155c7 100644
--- a/simulate/simulate.cc
+++ b/simulate/simulate.cc
@@ -1553,7 +1553,7 @@ void UiEvent(mjuiState* state) {
   if (state->type==mjEVENT_KEY && state->key!=0) {
     switch (state->key) {
     case ' ':                   // Mode
-      if (!sim->is_passive_ && sim->m_) {
+      if (sim->m_ || sim->is_passive_) {
         sim->run = 1 - sim->run;
         sim->pert.active = 0;
 
@@ -2122,7 +2122,7 @@ void Simulate::Sync() {
   // clear timers once profiler info has been copied
   ClearTimers(d_);
 
-  if (this->run || this->is_passive_) {
+  if (this->run) {
     // clear old perturbations, apply new
     mju_zero(d_->xfrc_applied, 6*m_->nbody);
     mjv_applyPerturbPose(m_, d_, &this->pert, 0);  // mocap bodies only
diff --git a/simulate/simulate.h b/simulate/simulate.h
index cd654192e5..81530cbebc 100644
--- a/simulate/simulate.h
+++ b/simulate/simulate.h
@@ -289,7 +289,7 @@ class Simulate {
   // simulation section of UI
   const mjuiDef def_simulation[14] = {
     {mjITEM_SECTION,   "Simulation",    mjPRESERVE, nullptr,     "AS"},
-    {mjITEM_RADIO,     "",              5, &this->run,           "Pause\nRun"},
+    {mjITEM_RADIO,     "",              2, &this->run,           "Pause\nRun"},
     {mjITEM_BUTTON,    "Reset",         2, nullptr,              " #259"},
     {mjITEM_BUTTON,    "Reload",        5, nullptr,              "CL"},
     {mjITEM_BUTTON,    "Align",         2, nullptr,              "CA"},