diff --git a/wp-includes/formatting.php b/wp-includes/formatting.php
index 5faac073da..cb3ddacaf8 100644
--- a/wp-includes/formatting.php
+++ b/wp-includes/formatting.php
@@ -1057,7 +1057,7 @@ function wp_richedit_pre($text) {
 
 function clean_url( $url ) {
 	if ('' == $url) return $url;
-	$url = preg_replace('|[^a-z0-9-~+_.?#=&;,/:%]|i', '', $url);
+	$url = preg_replace('|[^a-z0-9-~+_.?#=!&;,/:%]|i', '', $url);
 	$strip = array('%0d', '%0a');
 	$url = str_replace($strip, '', $url);
 	$url = str_replace(';//', '://', $url);