diff --git a/Lib/fontTools/varLib/interpolatable.py b/Lib/fontTools/varLib/interpolatable.py
index 39e7416f7..f0b1aa8b0 100644
--- a/Lib/fontTools/varLib/interpolatable.py
+++ b/Lib/fontTools/varLib/interpolatable.py
@@ -241,22 +241,24 @@ def test(glyphsets, glyphs=None, names=None, ignore_missing=False):
                     mask = (1 << n) - 1
                     isomorphisms = []
                     contourIsomorphisms.append(isomorphisms)
+                    complexPoints = [complex(*pt) for pt, bl in points.value]
                     for i in range(n):
                         b = ((bits << i) & mask) | ((bits >> (n - i)))
                         if b == bits:
                             isomorphisms.append(
-                                _rot_list([complex(*pt) for pt, bl in points.value], i)
+                                _rot_list(complexPoints, i)
                             )
                     # Add mirrored rotations
                     mirrored = list(reversed(points.value))
                     reversed_bits = 0
                     for pt, b in mirrored:
                         reversed_bits = (reversed_bits << 1) | b
+                    complexPoints = list(reversed(complexPoints))
                     for i in range(n):
                         b = ((reversed_bits << i) & mask) | ((reversed_bits >> (n - i)))
                         if b == bits:
                             isomorphisms.append(
-                                _rot_list([complex(*pt) for pt, bl in mirrored], i)
+                                _rot_list(complexPoints, i)
                             )
 
             # m0idx should be the index of the first non-None item in allNodeTypes,