diff --git a/api/onnx_web/chain/blend_img2img.py b/api/onnx_web/chain/blend_img2img.py
index 43568216..3257ffc5 100644
--- a/api/onnx_web/chain/blend_img2img.py
+++ b/api/onnx_web/chain/blend_img2img.py
@@ -23,7 +23,7 @@ def blend_img2img(
     *,
     strength: float,
     prompt: Optional[str] = None,
-    callback: ProgressCallback,
+    callback: ProgressCallback = None,
     **kwargs,
 ) -> Image.Image:
     prompt = prompt or params.prompt
diff --git a/api/onnx_web/chain/blend_inpaint.py b/api/onnx_web/chain/blend_inpaint.py
index 9531f439..b828fac9 100644
--- a/api/onnx_web/chain/blend_inpaint.py
+++ b/api/onnx_web/chain/blend_inpaint.py
@@ -29,7 +29,7 @@ def blend_inpaint(
     fill_color: str = "white",
     mask_filter: Callable = mask_filter_none,
     noise_source: Callable = noise_source_histogram,
-    callback: ProgressCallback,
+    callback: ProgressCallback = None,
     **kwargs,
 ) -> Image.Image:
     logger.info("upscaling image by expanding borders", expand)
diff --git a/api/onnx_web/chain/upscale_outpaint.py b/api/onnx_web/chain/upscale_outpaint.py
index 25e87173..7872930c 100644
--- a/api/onnx_web/chain/upscale_outpaint.py
+++ b/api/onnx_web/chain/upscale_outpaint.py
@@ -30,7 +30,7 @@ def upscale_outpaint(
     fill_color: str = "white",
     mask_filter: Callable = mask_filter_none,
     noise_source: Callable = noise_source_histogram,
-    callback: ProgressCallback,
+    callback: ProgressCallback = None,
     **kwargs,
 ) -> Image.Image:
     prompt = prompt or params.prompt
diff --git a/api/onnx_web/chain/upscale_stable_diffusion.py b/api/onnx_web/chain/upscale_stable_diffusion.py
index 69654e94..e947717d 100644
--- a/api/onnx_web/chain/upscale_stable_diffusion.py
+++ b/api/onnx_web/chain/upscale_stable_diffusion.py
@@ -67,7 +67,7 @@ def upscale_stable_diffusion(
     *,
     upscale: UpscaleParams,
     prompt: str = None,
-    callback: ProgressCallback,
+    callback: ProgressCallback = None,
     **kwargs,
 ) -> Image.Image:
     prompt = prompt or params.prompt