diff --git a/src/diffusers/image_processor.py b/src/diffusers/image_processor.py
index 4d8d73c863ae..c70a2ac331e7 100644
--- a/src/diffusers/image_processor.py
+++ b/src/diffusers/image_processor.py
@@ -533,7 +533,7 @@ def preprocess(
 
         if not is_valid_image_imagelist(image):
             raise ValueError(
-                f"Input is in incorrect format. Currently, we only support {', '.join(supported_formats)}"
+                f"Input is in incorrect format. Currently, we only support {', '.join(str(x) for x in supported_formats)}"
             )
         if not isinstance(image, list):
             image = [image]