diff --git a/Lib/fontTools/otlLib/builder.py b/Lib/fontTools/otlLib/builder.py
index c0dc69997..c7b753b8d 100644
--- a/Lib/fontTools/otlLib/builder.py
+++ b/Lib/fontTools/otlLib/builder.py
@@ -618,7 +618,7 @@ class ClassDefBuilder(object):
         # we should determine the encoded size. If the glyphs in a large
         # class form a contiguous range, the encoding is actually quite
         # compact, whereas a non-contiguous set might need a lot of bytes
-        # in the output file. We don't get this right with key=len below.
+        # in the output file. We don't get this right with the key below.
         result = sorted(self.classes_, key=lambda s: (len(s), s), reverse=True)
         if not self.useClass0_:
             result.insert(0, frozenset())