Ticket #40169: 40169.diff

src/wp-includes/ms-functions.php

@@ -415 +415 @@
         $orig_username = $user_name;
         $user_name = preg_replace( '/\s+/', '', sanitize_user( $user_name, true ) );
 
-        if ( $user_name != $orig_username || preg_match( '/[^a-z0-9]/', $user_name ) ) {
+        if ( $user_name != $orig_username || preg_match( '/[^a-z0-9 _.\-@]/', $user_name ) ) {
                 $errors->add( 'user_name', __( 'Usernames can only contain lowercase letters (a-z) and numbers.' ) );
                 $user_name = $orig_username;
         }