diff --git a/compiler/base/geometry.py b/compiler/base/geometry.py
index b766b1af..33bcaaa2 100644
--- a/compiler/base/geometry.py
+++ b/compiler/base/geometry.py
@@ -147,8 +147,12 @@ class instance(geometry):
             self.width = 0
             self.height = 0
         else:
-            self.width = round_to_grid(mod.width)
-            self.height = round_to_grid(mod.height)
+            if mirror in ["R90","R270"] or rotate in [90,270]:
+                self.width = round_to_grid(mod.height)
+                self.height = round_to_grid(mod.width)
+            else:
+                self.width = round_to_grid(mod.width)
+                self.height = round_to_grid(mod.height)
         self.compute_boundary(offset,mirror,rotate)
         
         debug.info(4, "creating instance: " + self.name)