diff --git a/airflow/models/serialized_dag.py b/airflow/models/serialized_dag.py
index 3e1ec0c70cce3..53e5e2ccbd223 100644
--- a/airflow/models/serialized_dag.py
+++ b/airflow/models/serialized_dag.py
@@ -251,7 +251,7 @@ def remove_deleted_dags(
                     cls.fileloc_hash.notin_(alive_fileloc_hashes),
                     cls.fileloc.notin_(alive_dag_filelocs),
                     or_(
-                        cls.processor_subdir is None,
+                        cls.processor_subdir.is_(None),
                         cls.processor_subdir == processor_subdir,
                     ),
                 )
diff --git a/tests/models/test_serialized_dag.py b/tests/models/test_serialized_dag.py
index d4e7d4e92316f..b425cd8f658cd 100644
--- a/tests/models/test_serialized_dag.py
+++ b/tests/models/test_serialized_dag.py
@@ -169,7 +169,7 @@ def test_remove_dags_by_filepath(self):
         # remove repeated files for those DAGs that define multiple dags in the same file (set comprehension)
         example_dag_files = list({dag.fileloc for dag in filtered_example_dags_list})
         example_dag_files.remove(dag_removed_by_file.fileloc)
-        SDM.remove_deleted_dags(example_dag_files)
+        SDM.remove_deleted_dags(example_dag_files, processor_subdir="/tmp/test")
         assert not SDM.has_dag(dag_removed_by_file.dag_id)
 
     def test_bulk_sync_to_db(self):