diff --git a/src/strings/strings.go b/src/strings/strings.go
index 1805a14bd2b..e3fdd9feaff 100644
--- a/src/strings/strings.go
+++ b/src/strings/strings.go
@@ -550,7 +550,7 @@ func Repeat(s string, count int) string {
 	return b.String()
 }
 
-// ToUpper returns a copy of the string s with all Unicode letters mapped to their upper case.
+// ToUpper returns s with all Unicode letters mapped to their upper case.
 func ToUpper(s string) string {
 	isASCII, hasLower := true, false
 	for i := 0; i < len(s); i++ {
@@ -580,7 +580,7 @@ func ToUpper(s string) string {
 	return Map(unicode.ToUpper, s)
 }
 
-// ToLower returns a copy of the string s with all Unicode letters mapped to their lower case.
+// ToLower returns s with all Unicode letters mapped to their lower case.
 func ToLower(s string) string {
 	isASCII, hasUpper := true, false
 	for i := 0; i < len(s); i++ {