diff --git a/awx/api/serializers.py b/awx/api/serializers.py
index 5eab0bea9a..572b4246ad 100644
--- a/awx/api/serializers.py
+++ b/awx/api/serializers.py
@@ -2234,8 +2234,9 @@ class JobLaunchSerializer(BaseSerializer):
             except (ValueError, TypeError):
                 try:
                     extra_vars = yaml.safe_load(extra_vars)
-                except (yaml.YAMLError, TypeError, AttributeError):
-                    errors['extra_vars'] = 'Must be valid JSON or YAML'
+                    assert isinstance(extra_vars, dict)
+                except (yaml.YAMLError, TypeError, AttributeError, AssertionError):
+                    errors['extra_vars'] = 'Must be a valid JSON or YAML dictionary'
 
         if not isinstance(extra_vars, dict):
             extra_vars = {}
diff --git a/awx/main/tests/functional/api/test_job_runtime_params.py b/awx/main/tests/functional/api/test_job_runtime_params.py
index a1069da198..6f76fdf1b6 100644
--- a/awx/main/tests/functional/api/test_job_runtime_params.py
+++ b/awx/main/tests/functional/api/test_job_runtime_params.py
@@ -159,7 +159,7 @@ def test_job_reject_invalid_prompted_extra_vars(runtime_data, job_template_promp
         dict(extra_vars='{"unbalanced brackets":'), user('admin', True))
 
     assert response.status_code == 400
-    assert response.data['extra_vars'] == ['Must be valid JSON or YAML']
+    assert response.data['extra_vars'] == ['Must be a valid JSON or YAML dictionary']
 
 @pytest.mark.django_db
 @pytest.mark.job_runtime_vars