diff --git a/wp-includes/functions.php b/wp-includes/functions.php
index 48f53f825b..b6bd681fd6 100644
--- a/wp-includes/functions.php
+++ b/wp-includes/functions.php
@@ -1188,12 +1188,12 @@ function wp_check_filetype( $filename, $mimes = null ) {
 		'asf|asx|wax|wmv|wmx' => 'video/asf',
 		'avi' => 'video/avi',
 		'mov|qt' => 'video/quicktime',
-		'mpeg|mpg|mpe' => 'video/mpeg',
+		'mpeg|mpg|mpe|mp4' => 'video/mpeg',
 		'txt|c|cc|h' => 'text/plain',
 		'rtx' => 'text/richtext',
 		'css' => 'text/css',
 		'htm|html' => 'text/html',
-		'mp3|mp4' => 'audio/mpeg',
+		'mp3|m4a' => 'audio/mpeg',
 		'ra|ram' => 'audio/x-realaudio',
 		'wav' => 'audio/wav',
 		'ogg' => 'audio/ogg',
diff --git a/wp-includes/post.php b/wp-includes/post.php
index a98bae3ecd..edfb412ab7 100644
--- a/wp-includes/post.php
+++ b/wp-includes/post.php
@@ -2390,9 +2390,8 @@ function wp_mime_type_icon( $mime = 0 ) {
 			$post_mimes[] = str_replace('/', '_', $mime);
 		}
 
-		$post_mimes[] = 'default';
-
 		$matches = wp_match_mime_types(array_keys($types), $post_mimes);
+		$matches['default'] = array('default');
 
 		foreach ( $matches as $match => $wilds ) {
 			if ( isset($types[$wilds[0]])) {