diff --git a/potassium/potassium.py b/potassium/potassium.py
index b4952cd..2cce945 100644
--- a/potassium/potassium.py
+++ b/potassium/potassium.py
@@ -158,6 +158,7 @@ def _handle_generic(self, endpoint, flask_request):
             res = make_response()
             res.status_code = 400
             res.headers['X-Endpoint-Type'] = endpoint.type
+            self._gpu_lock.release()
             return res
 
         if endpoint.type == "handler":
diff --git a/tests/test_endpoints.py b/tests/test_endpoints.py
index 6e621a6..d3f2fd6 100644
--- a/tests/test_endpoints.py
+++ b/tests/test_endpoints.py
@@ -47,6 +47,14 @@ def handler2_id(context: dict, request: potassium.Request) -> potassium.Response
     assert res.status_code == 200
     assert res.json == {"hello": "some_path/child_path"}
 
+    res = client.post("/", data='{"key": unquoted_value}', content_type='application/json')
+    assert res.status_code == 400
+    # check status
+    res = client.get("/__status__")
+    assert res.status_code == 200
+    assert res.json is not None
+    assert res.json["gpu_available"] == True
+
 # parameterized test for path collisions
 @pytest.mark.parametrize("paths", [
     ("/", "",),