diff --git a/python_modules/dagster/dagster/_core/definitions/multi_dimensional_partitions.py b/python_modules/dagster/dagster/_core/definitions/multi_dimensional_partitions.py
index 68ccf339fa5ce..2cc6b6ab6cdad 100644
--- a/python_modules/dagster/dagster/_core/definitions/multi_dimensional_partitions.py
+++ b/python_modules/dagster/dagster/_core/definitions/multi_dimensional_partitions.py
@@ -425,13 +425,11 @@ def get_tags_for_partition_key(self, partition_key: str) -> Mapping[str, str]:
 
     @property
     def time_window_dimension(self) -> PartitionDimensionDefinition:
-        check.invariant(self.has_time_window_dimension, "Must have time window dimension")
-        check.inst(
-            self.primary_dimension.partitions_def,
-            TimeWindowPartitionsDefinition,
-            "Sanity check that assumption that primary is time-windowed if it exists",
+        time_window_dims = self._get_time_window_dims()
+        check.invariant(
+            len(time_window_dims) == 1, "Expected exactly one time window partitioned dimension"
         )
-        return self.primary_dimension
+        return next(iter(time_window_dims))
 
     def _get_time_window_dims(self) -> List[PartitionDimensionDefinition]:
         return [