diff --git a/api/onnx_web/upscale.py b/api/onnx_web/upscale.py
index 66cdda26..46061c91 100644
--- a/api/onnx_web/upscale.py
+++ b/api/onnx_web/upscale.py
@@ -41,6 +41,7 @@ class ONNXImage():
 
     def clamp_(self, min, max):
         self.source = np.clip(self.source, min, max)
+        return self
 
     def numpy(self):
         return self.source