diff --git a/wp-app.php b/wp-app.php
index b47ee21da..2791ee726 100644
--- a/wp-app.php
+++ b/wp-app.php
@@ -403,7 +403,7 @@ EOD;
 			$slug = sanitize_file_name( $_SERVER['HTTP_TITLE'] );
 		elseif ( empty( $slug ) ) // just make a random name
 			$slug = substr( md5( uniqid( microtime() ) ), 0, 7);
-		$ext = preg_replace( '|.*/([a-z]+)|', '$1', $_SERVER['CONTENT_TYPE'] );
+		$ext = preg_replace( '|.*/([a-z0-9]+)|', '$1', $_SERVER['CONTENT_TYPE'] );
 		$slug = "$slug.$ext";
 		$file = wp_upload_bits( $slug, NULL, $bits);