diff --git a/python/cudf/cudf/core/column/datetime.py b/python/cudf/cudf/core/column/datetime.py
index 04d227b0faa..64ddcae72a7 100644
--- a/python/cudf/cudf/core/column/datetime.py
+++ b/python/cudf/cudf/core/column/datetime.py
@@ -278,10 +278,8 @@ def _validate_fillna_value(
             isinstance(fill_value, np.datetime64)
             and self.time_unit != np.datetime_data(fill_value)[0]
         ):
-            # TODO: Disallow this cast
             fill_value = fill_value.astype(self.dtype)
         elif isinstance(fill_value, str) and fill_value.lower() == "nat":
-            # TODO: Disallow this casting; user should be explicit
             fill_value = np.datetime64(fill_value, self.time_unit)
         return super()._validate_fillna_value(fill_value)
 
diff --git a/python/cudf/cudf/core/column/timedelta.py b/python/cudf/cudf/core/column/timedelta.py
index 7f2bb52b731..654d2c2b800 100644
--- a/python/cudf/cudf/core/column/timedelta.py
+++ b/python/cudf/cudf/core/column/timedelta.py
@@ -152,10 +152,8 @@ def _validate_fillna_value(
             isinstance(fill_value, np.timedelta64)
             and self.time_unit != np.datetime_data(fill_value)[0]
         ):
-            # TODO: Disallow this cast
             fill_value = fill_value.astype(self.dtype)
         elif isinstance(fill_value, str) and fill_value.lower() == "nat":
-            # TODO: Disallow this casting; user should be explicit
             fill_value = np.timedelta64(fill_value, self.time_unit)
         return super()._validate_fillna_value(fill_value)