diff --git a/lib/python/psr_utils.py b/lib/python/psr_utils.py
index 8880b5582..6106b4ecd 100644
--- a/lib/python/psr_utils.py
+++ b/lib/python/psr_utils.py
@@ -1031,7 +1031,7 @@ def rotate(arr, bins):
     rotate(arr, bins):
         Return an array rotated by 'bins' places to the left
     """
-    bins = int(bins % len(arr))
+    bins = int(bins) % len(arr)
     if bins==0:
         return arr
     else: