diff --git a/Lib/ufo2ft/featureWriters/kernFeatureWriter2.py b/Lib/ufo2ft/featureWriters/kernFeatureWriter2.py
index deb92ec4..de4eb663 100644
--- a/Lib/ufo2ft/featureWriters/kernFeatureWriter2.py
+++ b/Lib/ufo2ft/featureWriters/kernFeatureWriter2.py
@@ -251,6 +251,7 @@ def getKerningPairs(font, side1Classes, side2Classes, glyphSet=None, options=Non
                 glyphSet or {},
                 options or SimpleNamespace(**KernFeatureWriter.options),
             )
+            pairs.sort()
             side1toClass: Mapping[tuple[str, ...], ast.GlyphClassDefinition] = {
                 tuple(
                     glyph