diff --git a/wp-includes/functions.php b/wp-includes/functions.php
index 6876ff8c60..d34c9c099e 100644
--- a/wp-includes/functions.php
+++ b/wp-includes/functions.php
@@ -1120,7 +1120,7 @@ function wp_upload_dir( $time = NULL ) {
 
 // return a filename that is sanitized and unique for the given directory
 function wp_unique_filename( $dir, $filename, $unique_filename_callback = NULL ) {
-
+	$filename = strtolower( $filename );
 	// separate the filename into a name and extension
 	$info = pathinfo($filename);
 	$ext = $info['extension'];
diff --git a/wp-includes/media.php b/wp-includes/media.php
index b6227c321a..07f290b017 100644
--- a/wp-includes/media.php
+++ b/wp-includes/media.php
@@ -366,6 +366,7 @@ function gallery_shortcode($attr) {
 				border: 2px solid #cfcfcf;
 			}
 		</style>
+		<!-- see gallery_shortcode() in wp-includes/media.php -->
 		<div class='gallery'>");
 
 	foreach ( $attachments as $id => $attachment ) {