diff --git a/kraken/lib/segmentation.py b/kraken/lib/segmentation.py
index 3ab6008a1..d0b986fe0 100644
--- a/kraken/lib/segmentation.py
+++ b/kraken/lib/segmentation.py
@@ -498,7 +498,7 @@ def _calc_seam(baseline, polygon, angle, im_feats, bias=150):
         mask[line_locs] = 0
     dist_bias = distance_transform_cdt(mask)
     # absolute mask
-    mask = np.array(make_polygonal_mask(polygon-(r_min, c_min)), patch.shape[1::-1]) > 128
+    mask = np.array(make_polygonal_mask(polygon-(r_min, c_min), patch.shape[::-1])) > 128
     # dilate mask to compensate for aliasing during rotation
     mask = binary_erosion(mask, border_value=True, iterations=2)
     # combine weights with features