diff --git a/scikits/image/morphology/grey.py b/scikits/image/morphology/grey.py
index 5592850f..ac41c4f1 100644
--- a/scikits/image/morphology/grey.py
+++ b/scikits/image/morphology/grey.py
@@ -189,8 +189,5 @@ def greyscale_black_top_hat(image, selem, out=None):
         raise NotImplementedError("Cannot perform white top hat in place.")
     dilated = greyscale_dilate(image, selem)
     out = greyscale_erode(dilated, selem, out=out)
-
     out = out - image
-    if image is out:
-        raise NotImplementedError("Cannot perform black top hat in place.")
     return out