diff --git a/masque/file/gdsii.py b/masque/file/gdsii.py
index 8be0539..a9b7e98 100644
--- a/masque/file/gdsii.py
+++ b/masque/file/gdsii.py
@@ -414,6 +414,7 @@ def _subpatterns_to_refs(subpatterns: List[SubPattern or GridRepetition]
         elif mirror_y:
             ref.angle += 180
             ref.strans = set_bit(ref.strans, 15 - 0, True)
+        ref.angle %= 360
         ref.mag = subpat.scale
 
         refs.append(ref)