diff --git a/wp-includes/functions.php b/wp-includes/functions.php
index fcbe86e5b3..30cb0d6161 100644
--- a/wp-includes/functions.php
+++ b/wp-includes/functions.php
@@ -246,34 +246,31 @@ function maybe_unserialize( $original ) {
  */
 function is_serialized( $data ) {
 	// if it isn't a string, it isn't serialized
-	if ( !is_string( $data ) )
+	if ( ! is_string( $data ) )
 		return false;
 	$data = trim( $data );
  	if ( 'N;' == $data )
 		return true;
-	if ( function_exists('strpbrk') ) {
-		if ( strlen($data) > 1 && strpbrk($data,'adObis') == $data && $data[1] == ':' ) {
-			$badions = array();
-			$badions[1] = $data[0];
-		} else {
-			return false;
-		}
-	} elseif ( !preg_match( '/^([adObis]):/', $data, $badions ) ) {
+	$length = strlen( $data );
+	if ( $length < 4 )
 		return false;
-	}
-	switch ( $badions[1] ) {
+	if ( ':' !== $data[1] )
+		return false;
+	$lastc = $data[$length-1];
+	if ( ';' !== $lastc && '}' !== $lastc )
+		return false;
+	$token = $data[0];
+	switch ( $token ) {
+		case 's' :
+			if ( '"' !== $data[$length-2] )
+				return false;
 		case 'a' :
 		case 'O' :
-		case 's' :
-			if ( preg_match( "/^{$badions[1]}:[0-9]+:.*[;}]\$/s", $data ) )
-				return true;
-			break;
+			return (bool) preg_match( "/^{$token}:[0-9]+:/s", $data );
 		case 'b' :
 		case 'i' :
 		case 'd' :
-			if ( preg_match( "/^{$badions[1]}:[0-9.E-]+;\$/", $data ) )
-				return true;
-			break;
+			return (bool) preg_match( "/^{$token}:[0-9.E-]+;\$/", $data );
 	}
 	return false;
 }