diff --git a/src/unicode/utf8/utf8.go b/src/unicode/utf8/utf8.go
index 180c008ed5..82fa7c0d4d 100644
--- a/src/unicode/utf8/utf8.go
+++ b/src/unicode/utf8/utf8.go
@@ -263,10 +263,7 @@ func DecodeLastRune(p []byte) (r rune, size int) {
 	// guard against O(n^2) behavior when traversing
 	// backwards through strings with long sequences of
 	// invalid UTF-8.
-	lim := end - UTFMax
-	if lim < 0 {
-		lim = 0
-	}
+	lim := max(end - UTFMax, 0)
 	for start--; start >= lim; start-- {
 		if RuneStart(p[start]) {
 			break
@@ -303,10 +300,7 @@ func DecodeLastRuneInString(s string) (r rune, size int) {
 	// guard against O(n^2) behavior when traversing
 	// backwards through strings with long sequences of
 	// invalid UTF-8.
-	lim := end - UTFMax
-	if lim < 0 {
-		lim = 0
-	}
+	lim := max(end - UTFMax, 0)
 	for start--; start >= lim; start-- {
 		if RuneStart(s[start]) {
 			break