diff --git a/src/Interpreter.hs b/src/Interpreter.hs
index bc25448f8..aaa8c16b0 100644
--- a/src/Interpreter.hs
+++ b/src/Interpreter.hs
@@ -68,6 +68,7 @@ run construct comparable cost algorithm = case runFree algorithm of
     recur (Args as') (Args bs') = annotate . Args $ zipWith diffTerms' as' bs'
     recur (VarDecl a') (VarDecl b') = annotate . VarDecl $ diffTerms' a' b'
     recur (VarAssignment a' as') (VarAssignment b' bs') = annotate $ VarAssignment (diffTerms' a' b') (diffTerms' as' bs')
+    recur (Operator a') (Operator b') = annotate $ Operator (zipWith diffTerms' a' b')
     recur (Switch a' as') (Switch b' bs') = annotate $ Switch (diffTerms' a' b') (alignWith (these (pure . Delete) (pure . Insert) diffTerms') as' bs')
     recur (Case a' as') (Case b' bs') = annotate $ Case (diffTerms' a' b') (diffTerms' as' bs')
     recur (Leaf _) (Leaf _) = pure $ Replace (cofree (annotation1 :< a)) (cofree (annotation2 :< b))