diff --git a/src/pkg/exp/locale/collate/collate.go b/src/pkg/exp/locale/collate/collate.go
index 5853b710c337f025980c6eee8d2fe98e5d040a9e..59507e55b2cc83f38750b604d34b4aa80a2dbace 100644
--- a/src/pkg/exp/locale/collate/collate.go
+++ b/src/pkg/exp/locale/collate/collate.go
@@ -86,6 +86,7 @@ type Collator struct {
 }
 
 // Locales returns the list of locales for which collating differs from its parent locale.
+// The returned value should not be modified.
 func Locales() []string {
 	return availableLocales
 }