diff --git a/crc/api/workflow.py b/crc/api/workflow.py
index 10fb3ce0..223f280f 100644
--- a/crc/api/workflow.py
+++ b/crc/api/workflow.py
@@ -91,7 +91,7 @@ def delete_workflow_specification(spec_id):
 
     # Delete all events and workflow models related to this specification
     for workflow in session.query(WorkflowModel).filter_by(workflow_spec_id=spec_id):
-        StudyService.delete_workflow(workflow)
+        StudyService.delete_workflow(workflow.id)
     session.query(WorkflowSpecModel).filter_by(id=spec_id).delete()
     session.commit()
 
diff --git a/crc/services/study_service.py b/crc/services/study_service.py
index 3befb382..fab76542 100644
--- a/crc/services/study_service.py
+++ b/crc/services/study_service.py
@@ -79,7 +79,7 @@ class StudyService(object):
     def delete_study(study_id):
         session.query(TaskEventModel).filter_by(study_id=study_id).delete()
         for workflow in session.query(WorkflowModel).filter_by(study_id=study_id):
-            StudyService.delete_workflow(workflow)
+            StudyService.delete_workflow(workflow.id)
         session.query(StudyModel).filter_by(id=study_id).delete()
         session.commit()