diff --git a/ants/utils/slice_image.py b/ants/utils/slice_image.py
index 6eafbf5a..05878693 100644
--- a/ants/utils/slice_image.py
+++ b/ants/utils/slice_image.py
@@ -7,7 +7,7 @@
 from .. import utils
 
 
-def slice_image(image, axis=None, idx=None, collapse_strategy=0):
+def slice_image(image, axis, idx, collapse_strategy=0):
     """
     Slice an image.