diff --git a/mdevaluate/pbc.py b/mdevaluate/pbc.py
index 14eb035..66c903b 100644
--- a/mdevaluate/pbc.py
+++ b/mdevaluate/pbc.py
@@ -250,11 +250,11 @@ def pbc_points(coordinates, box, thickness=0, index=False, shear=False):
     originals values.
     """
     if shear:
-        box[2, 0] = box[2, 0] % box[2, 2]
+        box[2, 0] = box[2, 0] % box[0, 0]
         # Shifts the box images in the other directions if they moved more than
         # half the box length
         if box[2, 0] > box[2, 2] / 2:
-            box[2, 0] = box[2, 0] - box[2, 2]
+            box[2, 0] = box[2, 0] - box[0, 0]
 
     grid = np.array(
         [[i, j, k] for k in [-1, 0, 1] for j in [1, 0, -1] for i in [-1, 0, 1]]