diff --git a/google/cloud/firestore_v1/base_collection.py b/google/cloud/firestore_v1/base_collection.py
index b74ced2a3..b113da827 100644
--- a/google/cloud/firestore_v1/base_collection.py
+++ b/google/cloud/firestore_v1/base_collection.py
@@ -128,7 +128,7 @@ def _aggregation_query(self) -> BaseAggregationQuery:
     def _vector_query(self) -> BaseVectorQuery:
         raise NotImplementedError
 
-    def document(self, document_id: Optional[str] = None):
+    def document(self, document_id: Optional[str] = None) -> DocumentReference:
         """Create a sub-document underneath the current collection.
 
         Args: