diff --git a/src/RWS.hs b/src/RWS.hs
index 288e4384f..e17e49548 100644
--- a/src/RWS.hs
+++ b/src/RWS.hs
@@ -59,6 +59,7 @@ rws :: (HasField fields (Maybe FeatureVector), Functor f, Eq1 f)
     -> RWSEditScript f fields
 rws _            _          as [] = This <$> as
 rws _            _          [] bs = That <$> bs
+rws _            canCompare [a] [b] | canCompareTerms canCompare a b = [These a b]
 rws editDistance canCompare as bs = Eff.run . RWS.run editDistance canCompare as bs $ do
   sesDiffs <- ses'
   (featureAs, featureBs, mappedDiffs, allDiffs) <- genFeaturizedTermsAndDiffs' sesDiffs