diff --git a/tensordict/base.py b/tensordict/base.py
index ef560b7fc..39729eba4 100644
--- a/tensordict/base.py
+++ b/tensordict/base.py
@@ -10965,7 +10965,7 @@ def set_(x):
                     tgt = mb_unwrap_functional_tensor(new_thing)
                     src = mb_unwrap_functional_tensor(ragged_source)
                     tgt.nested_int_memo = src.nested_int_memo
-                else:
+                elif new_thing is not None:
                     _tensor_symint_registry[new_thing] = _tensor_symint_registry[
                         ragged_source
                     ]