diff --git a/modules/api/api.py b/modules/api/api.py
index 4e6560826..3e42dd7b1 100644
--- a/modules/api/api.py
+++ b/modules/api/api.py
@@ -99,7 +99,7 @@ def decode_base64_to_image(encoding):
         raise HTTPException(status_code=500, detail="Invalid encoded image") from e
 
 
-def encode_pil_to_base64(image):
+def encode_pil_to_base64(image: Image.Image):
     with io.BytesIO() as output_bytes:
         if isinstance(image, str):
             return image
diff --git a/modules/postprocessing.py b/modules/postprocessing.py
index 9afcfef86..40cf866a4 100644
--- a/modules/postprocessing.py
+++ b/modules/postprocessing.py
@@ -66,7 +66,7 @@ def run_postprocessing(extras_mode, image, image_folder, input_dir, output_dir,
         if parameters:
             existing_pnginfo["parameters"] = parameters
 
-        initial_pp = scripts_postprocessing.PostprocessedImage(image_data)
+        initial_pp = scripts_postprocessing.PostprocessedImage(image_data.convert("RGBA")) if image_data.mode == "RGBA" else scripts_postprocessing.PostprocessedImage(image_data.convert("RGB"))
 
         scripts.scripts_postproc.run(initial_pp, args)