diff --git a/mk2rbc/expr.go b/mk2rbc/expr.go
index 07f7ca1..dc16d1d 100644
--- a/mk2rbc/expr.go
+++ b/mk2rbc/expr.go
@@ -595,6 +595,7 @@
 	for i, arg := range cx.args {
 		argsCopy[i] = arg.transform(transformer)
 	}
+	cx.args = argsCopy
 	if replacement := transformer(cx); replacement != nil {
 		return replacement
 	} else {