diff --git a/src/bytes/bytes.go b/src/bytes/bytes.go
index 260f32500a0fc2f29c15b2928daefa1cf3acb84b..9af177fa882d7e17376649395721e183332211e3 100644
--- a/src/bytes/bytes.go
+++ b/src/bytes/bytes.go
@@ -144,6 +144,10 @@ func IndexRune(s []byte, r rune) int {
 // code points in chars. It returns -1 if chars is empty or if there is no code
 // point in common.
 func IndexAny(s []byte, chars string) int {
+	if chars == "" {
+		// Avoid scanning all of s.
+		return -1
+	}
 	if len(s) > 8 {
 		if as, isASCII := makeASCIISet(chars); isASCII {
 			for i, c := range s {
@@ -176,6 +180,10 @@ func IndexAny(s []byte, chars string) int {
 // the Unicode code points in chars. It returns -1 if chars is empty or if
 // there is no code point in common.
 func LastIndexAny(s []byte, chars string) int {
+	if chars == "" {
+		// Avoid scanning all of s.
+		return -1
+	}
 	if len(s) > 8 {
 		if as, isASCII := makeASCIISet(chars); isASCII {
 			for i := len(s) - 1; i >= 0; i-- {
diff --git a/src/bytes/example_test.go b/src/bytes/example_test.go
index 00e39cadcbef6de21f1c952562d2d495cb311dbe..5b7a46058f5c73b44ec111b411d9580ae5c3f7ff 100644
--- a/src/bytes/example_test.go
+++ b/src/bytes/example_test.go
@@ -155,7 +155,7 @@ func ExampleCount() {
 
 func ExampleEqual() {
 	fmt.Println(bytes.Equal([]byte("Go"), []byte("Go")))
-	fmt.Println(bytes.Equal([]byte("Go"), []byte("go")))
+	fmt.Println(bytes.Equal([]byte("Go"), []byte("C++")))
 	// Output:
 	// true
 	// false
diff --git a/src/strings/strings.go b/src/strings/strings.go
index c66c248c023f2732bf0e8d960cce1bee26f0566f..02c032046b7bc67247b11ef70d691cdbe51634f2 100644
--- a/src/strings/strings.go
+++ b/src/strings/strings.go
@@ -166,6 +166,10 @@ func IndexRune(s string, r rune) int {
 // IndexAny returns the index of the first instance of any Unicode code point
 // from chars in s, or -1 if no Unicode code point from chars is present in s.
 func IndexAny(s, chars string) int {
+	if chars == "" {
+		// Avoid scanning all of s.
+		return -1
+	}
 	if len(s) > 8 {
 		if as, isASCII := makeASCIISet(chars); isASCII {
 			for i := 0; i < len(s); i++ {
@@ -190,6 +194,10 @@ func IndexAny(s, chars string) int {
 // point from chars in s, or -1 if no Unicode code point from chars is
 // present in s.
 func LastIndexAny(s, chars string) int {
+	if chars == "" {
+		// Avoid scanning all of s.
+		return -1
+	}
 	if len(s) > 8 {
 		if as, isASCII := makeASCIISet(chars); isASCII {
 			for i := len(s) - 1; i >= 0; i-- {