diff --git a/masque/file/gdsii.py b/masque/file/gdsii.py
index b5b5a13..5a891ef 100644
--- a/masque/file/gdsii.py
+++ b/masque/file/gdsii.py
@@ -439,8 +439,10 @@ def _subpatterns_to_refs(subpatterns: List[SubPattern or GridRepetition]
     for subpat in subpatterns:
         encoded_name = subpat.pattern.name
 
+        # Note: GDS mirrors first and rotates second
+        mirror_x, extra_angle = normalize_mirror(subpat.mirrored)
         if isinstance(subpat, GridRepetition):
-            mirror_signs = (-1) ** numpy.array(subpat.mirrored)
+            mirror_signs = [(-1 if mirror_x else 1), 1]
             xy = numpy.array(subpat.offset) + [
                   [0, 0],
                   numpy.dot(rotation_matrix_2d(subpat.rotation), subpat.a_vector * mirror_signs) * subpat.scale * subpat.a_count,
@@ -454,7 +456,6 @@ def _subpatterns_to_refs(subpatterns: List[SubPattern or GridRepetition]
             ref = gdsii.elements.SRef(struct_name=encoded_name,
                                       xy=numpy.round([subpat.offset]).astype(int))
 
-        mirror_x, extra_angle = normalize_mirror(subpat.mirrored)
         ref.angle = ((subpat.rotation + extra_angle) * 180 / numpy.pi) % 360
         #  strans must be non-None for angle and mag to take effect
         ref.strans = set_bit(0, 15 - 0, mirror_x)
diff --git a/masque/repetition.py b/masque/repetition.py
index faea08f..6349662 100644
--- a/masque/repetition.py
+++ b/masque/repetition.py
@@ -281,6 +281,10 @@ class GridRepetition:
         :return: self
         """
         self.mirrored[axis] = not self.mirrored[axis]
+        self.rotation *= -1
+        self.a_vector[axis] *= -1
+        if self.b_vector is not None:
+            self.b_vector[axis] *= -1
         return self
 
     def get_bounds(self) -> numpy.ndarray or None:
diff --git a/masque/subpattern.py b/masque/subpattern.py
index d18bc36..b8441d5 100644
--- a/masque/subpattern.py
+++ b/masque/subpattern.py
@@ -181,6 +181,7 @@ class SubPattern:
         :return: self
         """
         self.mirrored[axis] = not self.mirrored[axis]
+        self.rotation *= -1
         return self
 
     def get_bounds(self) -> numpy.ndarray or None: