diff --git a/wp-includes/theme.php b/wp-includes/theme.php
index 2ba2f3d4ee..3d7cddbd23 100644
--- a/wp-includes/theme.php
+++ b/wp-includes/theme.php
@@ -505,18 +505,18 @@ function preview_theme() {
 	if ( !current_user_can( 'switch_themes' ) )
 		return;
 
-	$_GET[template] = preg_replace('|[^a-z0-9_.-]|i', '', $_GET[template]);
+	$_GET['template'] = preg_replace('|[^a-z0-9_.-]|i', '', $_GET['template']);
 
-	if ( validate_file($_GET[template]) )
+	if ( validate_file($_GET['template']) )
 		return;
 
-	add_filter('template', create_function('', "return '$_GET[template]';") );
+	add_filter('template', create_function('', "return '{$_GET['template']}';") );
 
 	if ( isset($_GET['stylesheet']) ) {
-		$_GET[stylesheet] = preg_replace('|[^a-z0-9_.-]|i', '', $_GET[stylesheet]);
-		if ( validate_file($_GET[stylesheet]) )
+		$_GET['stylesheet'] = preg_replace('|[^a-z0-9_.-]|i', '', $_GET['stylesheet']);
+		if ( validate_file($_GET['stylesheet']) )
 			return;
-		add_filter('stylesheet', create_function('', "return '$_GET[stylesheet]';") );
+		add_filter('stylesheet', create_function('', "return '{$_GET['stylesheet']}';") );
 	}
 
 	ob_start( 'preview_theme_ob_filter' );