diff --git a/masque/builder/tools.py b/masque/builder/tools.py
index b771eac..04fb18e 100644
--- a/masque/builder/tools.py
+++ b/masque/builder/tools.py
@@ -506,7 +506,7 @@ class AutoTool(Tool, metaclass=ABCMeta):
             return numpy.zeros(2)
         orot = out_transition.our_port.rotation
         assert orot is not None
-        otrans_dxy = rotation_matrix_2d(-orot + bend_angle) @ (out_transition.their_port.offset - out_transition.our_port.offset)
+        otrans_dxy = rotation_matrix_2d(pi - orot - bend_angle) @ (out_transition.their_port.offset - out_transition.our_port.offset)
         return otrans_dxy
 
     def planL(