diff --git a/tensordict/_td.py b/tensordict/_td.py
index f27c6f3ac..2f67a025e 100644
--- a/tensordict/_td.py
+++ b/tensordict/_td.py
@@ -1246,8 +1246,8 @@ def _set_str(
         if not validated:
             value = self._validate_value(value, check_shape=True)
         if not inplace:
-            # if self.is_locked:
-            #     raise RuntimeError(_LOCK_ERROR)
+            if self.is_locked:
+                raise RuntimeError(_LOCK_ERROR)
             self._tensordict[key] = value
         else:
             try: