diff --git a/src/diffusers/pipeline_utils.py b/src/diffusers/pipeline_utils.py
index 8991bfcedb..5e7cf2d7a5 100644
--- a/src/diffusers/pipeline_utils.py
+++ b/src/diffusers/pipeline_utils.py
@@ -476,7 +476,7 @@ class DiffusionPipeline(ConfigMixin):
             for module in missing_modules:
                 init_kwargs[module] = passed_class_obj[module]
         elif len(missing_modules) > 0:
-            passed_modules = set(init_kwargs.keys() + passed_class_obj.keys())
+            passed_modules = set(list(init_kwargs.keys()) + list(passed_class_obj.keys()))
             raise ValueError(
                 f"Pipeline {pipeline_class} expected {expected_modules}, but only {passed_modules} were passed."
             )