diff --git a/wp-admin/admin-ajax.php b/wp-admin/admin-ajax.php
index 1c03ba8de4..fc4731a98c 100644
--- a/wp-admin/admin-ajax.php
+++ b/wp-admin/admin-ajax.php
@@ -93,10 +93,10 @@ case 'wp-compression-test' :
 		 } elseif ( 2 == $_GET['test'] ) {
 			if ( !isset($_SERVER['HTTP_ACCEPT_ENCODING']) )
 				die('-1');
-			if ( false !== strpos( strtolower($_SERVER['HTTP_ACCEPT_ENCODING']), 'deflate') && function_exists('gzdeflate') && ! $force_gzip ) {
+			if ( false !== stripos( $_SERVER['HTTP_ACCEPT_ENCODING'], 'deflate') && function_exists('gzdeflate') && ! $force_gzip ) {
 				header('Content-Encoding: deflate');
 				$out = gzdeflate( $test_str, 1 );
-			} elseif ( false !== strpos( strtolower($_SERVER['HTTP_ACCEPT_ENCODING']), 'gzip') && function_exists('gzencode') ) {
+			} elseif ( false !== stripos( $_SERVER['HTTP_ACCEPT_ENCODING'], 'gzip') && function_exists('gzencode') ) {
 				header('Content-Encoding: gzip');
 				$out = gzencode( $test_str, 1 );
 			} else {
diff --git a/wp-admin/includes/class-wp-filesystem-ftpext.php b/wp-admin/includes/class-wp-filesystem-ftpext.php
index 795242b0ad..d68d9eaac6 100644
--- a/wp-admin/includes/class-wp-filesystem-ftpext.php
+++ b/wp-admin/includes/class-wp-filesystem-ftpext.php
@@ -258,7 +258,7 @@ class WP_Filesystem_FTPext extends WP_Filesystem_Base {
 	function parselisting($line) {
 		static $is_windows;
 		if ( is_null($is_windows) )
-			$is_windows = strpos( strtolower( ftp_systype($this->link) ), 'win') !== false;
+			$is_windows = stripos( ftp_systype($this->link), 'win') !== false;
 
 		if ( $is_windows && preg_match('/([0-9]{2})-([0-9]{2})-([0-9]{2}) +([0-9]{2}):([0-9]{2})(AM|PM) +([0-9]+|<DIR>) +(.+)/', $line, $lucifer) ) {
 			$b = array();
diff --git a/wp-admin/includes/media.php b/wp-admin/includes/media.php
index 32eae42237..cdac6fde99 100644
--- a/wp-admin/includes/media.php
+++ b/wp-admin/includes/media.php
@@ -1382,7 +1382,7 @@ function media_upload_form( $errors = null ) {
 
 	// If Mac and mod_security, no Flash. :(
 	$flash = true;
-	if ( false !== strpos(strtolower($_SERVER['HTTP_USER_AGENT']), 'mac') && apache_mod_loaded('mod_security') )
+	if ( false !== stripos($_SERVER['HTTP_USER_AGENT'], 'mac') && apache_mod_loaded('mod_security') )
 		$flash = false;
 
 	$flash = apply_filters('flash_uploader', $flash);
diff --git a/wp-includes/general-template.php b/wp-includes/general-template.php
index 545c780bdf..279da70333 100644
--- a/wp-includes/general-template.php
+++ b/wp-includes/general-template.php
@@ -1146,7 +1146,7 @@ function get_calendar($initial = true, $echo = true) {
 		$daywithpost = array();
 	}
 
-	if (strpos($_SERVER['HTTP_USER_AGENT'], 'MSIE') !== false || strpos(strtolower($_SERVER['HTTP_USER_AGENT']), 'camino') !== false || strpos(strtolower($_SERVER['HTTP_USER_AGENT']), 'safari') !== false)
+	if (strpos($_SERVER['HTTP_USER_AGENT'], 'MSIE') !== false || stripos($_SERVER['HTTP_USER_AGENT'], 'camino') !== false || stripos($_SERVER['HTTP_USER_AGENT'], 'safari') !== false)
 		$ak_title_separator = "\n";
 	else
 		$ak_title_separator = ', ';
diff --git a/wp-includes/vars.php b/wp-includes/vars.php
index ec2be5e445..7a62c892ad 100644
--- a/wp-includes/vars.php
+++ b/wp-includes/vars.php
@@ -40,9 +40,9 @@ $is_lynx = $is_gecko = $is_winIE = $is_macIE = $is_opera = $is_NS4 = $is_safari
 if ( isset($_SERVER['HTTP_USER_AGENT']) ) {
 	if ( strpos($_SERVER['HTTP_USER_AGENT'], 'Lynx') !== false ) {
 		$is_lynx = true;
-	} elseif ( strpos(strtolower($_SERVER['HTTP_USER_AGENT']), 'chrome') !== false ) {
+	} elseif ( stripos($_SERVER['HTTP_USER_AGENT'], 'chrome') !== false ) {
 		$is_chrome = true;
-	} elseif ( strpos(strtolower($_SERVER['HTTP_USER_AGENT']), 'safari') !== false ) {
+	} elseif ( stripos($_SERVER['HTTP_USER_AGENT'], 'safari') !== false ) {
 		$is_safari = true;
 	} elseif ( strpos($_SERVER['HTTP_USER_AGENT'], 'Gecko') !== false ) {
 		$is_gecko = true;
@@ -57,7 +57,7 @@ if ( isset($_SERVER['HTTP_USER_AGENT']) ) {
 	}
 }
 
-if ( $is_safari && strpos(strtolower($_SERVER['HTTP_USER_AGENT']), 'mobile') !== false )
+if ( $is_safari && stripos($_SERVER['HTTP_USER_AGENT'], 'mobile') !== false )
 	$is_iphone = true;
 
 $is_IE = ( $is_macIE || $is_winIE );