diff --git a/api/onnx_web/chain/blend_mask.py b/api/onnx_web/chain/blend_mask.py
index 4486bbf6..326ba162 100644
--- a/api/onnx_web/chain/blend_mask.py
+++ b/api/onnx_web/chain/blend_mask.py
@@ -30,17 +30,16 @@ class BlendMaskStage(BaseStage):
     ) -> StageResult:
         logger.info("blending image using mask")
 
-        # TODO: does this need an alpha channel?
         mult_mask = Image.new(stage_mask.mode, stage_mask.size, color="black")
-        mult_mask.alpha_composite(stage_mask)
+        mult_mask = Image.alpha_composite(mult_mask, stage_mask)
         mult_mask = mult_mask.convert("L")
 
         if is_debug():
             save_image(server, "last-mask.png", stage_mask)
             save_image(server, "last-mult-mask.png", mult_mask)
 
-        return StageResult(
-            images=[
+        return StageResult.from_images(
+            [
                 Image.composite(stage_source, source, mult_mask)
                 for source in sources.as_image()
             ]