diff --git a/ffn/inference/movement.py b/ffn/inference/movement.py
index df567e8..4adf649 100644
--- a/ffn/inference/movement.py
+++ b/ffn/inference/movement.py
@@ -71,7 +71,7 @@ def get_scored_move_offsets(deltas, prob_map, threshold=0.9):
       # of the subvolume orthogonal to the current axis.
       face_sel = subvol_sel[:]
       face_sel[axis] = axis_offset + center[axis]
-      face_prob = prob_map[face_sel]
+      face_prob = prob_map[tuple(face_sel)]
       shape = face_prob.shape
 
       # Find voxel with maximum activation.