diff --git a/geometry.py b/geometry.py
index 3b78ff6ef2c0e59a9821830e52eeb07648e6748f..80ae249786b27597be612b9c517e727c74d17033 100644
--- a/geometry.py
+++ b/geometry.py
@@ -253,7 +253,7 @@ def add_black_and_white_image(boundary_handling, image_file, target_slice=None,
             image_target_slice = shift_slice(intersection_slice, [-s.start for s in image_slice])
             mask_target_slice = [mask_target_slice[i] if i in plane else slice(None, None) for i in range(dim)]
             image_target_slice = [image_target_slice[i] if i in plane else np.newaxis for i in range(dim)]
-            result[mask_target_slice] = zoomed_image[image_target_slice]
+            result[tuple(mask_target_slice)] = zoomed_image[image_target_slice]
             return result
 
     return boundary_handling.set_boundary(boundary, slice_obj=image_slice, mask_callback=callback,