diff --git a/python/mujoco/viewer.py b/python/mujoco/viewer.py
index 9784691f..67d65e89 100644
--- a/python/mujoco/viewer.py
+++ b/python/mujoco/viewer.py
@@ -298,6 +298,7 @@ def _physics_loop(simulate: _Simulate, loader: Optional[_InternalLoaderType]):
 
           # Run mj_forward, to update rendering and joint sliders.
           mujoco.mj_forward(m, d)
+          synccpu = time.time()
 
 
 def _launch_internal(
diff --git a/simulate/main.cc b/simulate/main.cc
index 55c09dee..509f4187 100644
--- a/simulate/main.cc
+++ b/simulate/main.cc
@@ -392,6 +392,7 @@ void PhysicsLoop(mj::Simulate& sim) {
         else {
           // run mj_forward, to update rendering and joint sliders
           mj_forward(m, d);
+          syncCPU = mj::Simulate::Clock::now();
         }
       }
     }  // release std::lock_guard<std::mutex>