diff --git a/masque/shapes/polygon.py b/masque/shapes/polygon.py
index dc5afa1..c9617a9 100644
--- a/masque/shapes/polygon.py
+++ b/masque/shapes/polygon.py
@@ -321,7 +321,7 @@ class Polygon(Shape):
             else:
                 raise PatternError('Two of ymin, yctr, ymax, ly must be None!')
 
-        poly = Polygon.rectangle(lx, ly, offset=(xctr, yctr), repetition=repetition)
+        poly = Polygon.rectangle(abs(lx), abs(ly), offset=(xctr, yctr), repetition=repetition)
         return poly
 
     @staticmethod