diff --git a/dexpreopt/dexpreopt.go b/dexpreopt/dexpreopt.go
index eacb86a..7fdfb49 100644
--- a/dexpreopt/dexpreopt.go
+++ b/dexpreopt/dexpreopt.go
@@ -578,9 +578,7 @@
 	}
 }
 
-func copyOf(l []string) []string {
-	return append([]string(nil), l...)
-}
+var copyOf = android.CopyOf
 
 func anyHavePrefix(l []string, prefix string) bool {
 	for _, x := range l {