diff --git a/Demo/sgi/video/imgconv.py b/Demo/sgi/video/imgconv.py
index 6e83806e0f1..a3a5d19d7a4 100755
--- a/Demo/sgi/video/imgconv.py
+++ b/Demo/sgi/video/imgconv.py
@@ -9,7 +9,7 @@ def null(img, x, y):
 	return img
 	
 def mono2grey(img, x, y):
-	imageop.mono2grey(img, x, y, 0, 255)
+	return imageop.mono2grey(img, x, y, 0, 255)
 
 converters = [ \
 	  ('grey',  'grey4', imageop.grey2grey4,   LOSSY), \