diff --git a/mjx/mujoco/mjx/viewer.py b/mjx/mujoco/mjx/viewer.py
index c4d7c607..0a1605a6 100644
--- a/mjx/mujoco/mjx/viewer.py
+++ b/mjx/mujoco/mjx/viewer.py
@@ -53,7 +53,7 @@ def _main(argv: Sequence[str]) -> None:
       start = time.time()
 
       # TODO(robotics-simulation): recompile when changing disable flags, etc.
-      dx = dx.replace(ctrl=d.ctrl, xfrc_applied=d.xfrc_applied)
+      dx = dx.replace(ctrl=d.ctrl, act=d.act, xfrc_applied=d.xfrc_applied)
       dx = dx.replace(qpos=d.qpos, qvel=d.qvel, time=d.time)  # handle resets
       mx = mx.tree_replace({
           'opt.gravity': m.opt.gravity,