diff --git a/opennsfw2/_inference.py b/opennsfw2/_inference.py
index 97cdb9b..1e1652d 100644
--- a/opennsfw2/_inference.py
+++ b/opennsfw2/_inference.py
@@ -108,6 +108,7 @@ def predict_images(
         from ._inspection import make_and_save_nsfw_grad_cam
 
         for image_handle, grad_cam_path in zip(image_handles, grad_cam_paths):
+            assert isinstance(image_handle, (str, Image.Image))  # For mypy.
             pil_image = _load_pil_image(image_handle)
             make_and_save_nsfw_grad_cam(
                 pil_image, preprocessing, global_model, grad_cam_path, alpha