diff --git a/atst/models/utils.py b/atst/models/utils.py
index fe0fe4f7..e7b69032 100644
--- a/atst/models/utils.py
+++ b/atst/models/utils.py
@@ -33,4 +33,4 @@ def claim_for_update(resource, minutes=30):
     finally:
         db.session.query(Model).filter(Model.id == resource.id).filter(
             Model.claimed_until != None
-        ).update({"claimed_until": sql.null()}, synchronize_session="fetch")
+        ).update({"claimed_until": None}, synchronize_session="fetch")
diff --git a/tests/test_jobs.py b/tests/test_jobs.py
index 13ebb89e..7973936e 100644
--- a/tests/test_jobs.py
+++ b/tests/test_jobs.py
@@ -288,4 +288,10 @@ def test_claim_for_update(session):
     t1.join()
     t2.join()
 
+    session.refresh(environment)
+
+    # Only FirstThread acquired a claim and wrote to satisfied_claims
     assert satisfied_claims == ["FirstThread"]
+
+    # The claim is released as soon as work is done
+    assert environment.claimed_until is None