diff --git a/wp-admin/admin-ajax.php b/wp-admin/admin-ajax.php
index 294bb49bc6..06df8afb45 100644
--- a/wp-admin/admin-ajax.php
+++ b/wp-admin/admin-ajax.php
@@ -25,7 +25,7 @@ if ( isset($_GET['action']) && 'ajax-tag-search' == $_GET['action'] ) {
 
 	$s = $_GET['q']; // is this slashed already?
 
-	if ( strstr( $s, ',' ) ) {
+	if ( false !== strpos( $s, ',' ) ) {
 		$s = explode( ',', $s );
 		$s = $s[count( $s ) - 1];
 	}
diff --git a/wp-includes/query.php b/wp-includes/query.php
index 9756f6c049..872f987db6 100644
--- a/wp-includes/query.php
+++ b/wp-includes/query.php
@@ -1752,7 +1752,7 @@ function setup_postdata($post) {
 	if ( is_single() || is_page() || is_feed() )
 		$more = 1;
 	$content = $post->post_content;
-	if ( preg_match('/<!--nextpage-->/', $content) ) {
+	if ( strpos( $content, '<!--nextpage-->' ) ) {
 		if ( $page > 1 )
 			$more = 1;
 		$multipage = 1;
diff --git a/wp-login.php b/wp-login.php
index b258c82138..f610b8cfcf 100644
--- a/wp-login.php
+++ b/wp-login.php
@@ -103,7 +103,7 @@ function retrieve_password() {
 	if ( empty( $_POST['user_login'] ) && empty( $_POST['user_email'] ) )
 		$errors->add('empty_username', __('<strong>ERROR</strong>: Enter a username or e-mail address.'));
 
-	if ( strstr($_POST['user_login'], '@') ) {
+	if ( strpos($_POST['user_login'], '@') ) {
 		$user_data = get_user_by_email(trim($_POST['user_login']));
 		if ( empty($user_data) )
 			$errors->add('invalid_email', __('<strong>ERROR</strong>: There is no user registered with that email address.'));
diff --git a/wp-mail.php b/wp-mail.php
index d3d9e00ac8..620201c7b0 100644
--- a/wp-mail.php
+++ b/wp-mail.php
@@ -60,7 +60,7 @@ for ($i=1; $i <= $count; $i++) :
 				$content_transfer_encoding = explode(';', $content_transfer_encoding);
 				$content_transfer_encoding = $content_transfer_encoding[0];
 			}
-			if (($content_type == 'multipart/alternative') && (preg_match('/boundary="/', $line)) && ($boundary == '')) {
+			if (($content_type == 'multipart/alternative') && (false !== strpos($line, 'boundary="')) && ($boundary == '')) {
 				$boundary = trim($line);
 				$boundary = explode('"', $boundary);
 				$boundary = $boundary[1];