Index: modules/user/user.module
===================================================================
RCS file: /cvs/drupal/drupal/modules/user/user.module,v
retrieving revision 1.904
diff -u -p -r1.904 user.module
--- modules/user/user.module	23 Apr 2008 20:01:56 -0000	1.904
+++ modules/user/user.module	26 Apr 2008 17:26:34 -0000
@@ -353,7 +353,7 @@ function user_validate_name($name) {
   if (substr($name, 0, 1) == ' ') return t('The username cannot begin with a space.');
   if (substr($name, -1) == ' ') return t('The username cannot end with a space.');
   if (strpos($name, '  ') !== FALSE) return t('The username cannot contain multiple spaces in a row.');
-  if (ereg("[^\x80-\xF7 [:alnum:]@_.-]", $name)) return t('The username contains an illegal character.');
+  if (ereg("[^\x80-\xF7 [:alnum:]@_.-']", $name)) return t('The username contains an illegal character.');
   if (preg_match('/[\x{80}-\x{A0}' .         // Non-printable ISO-8859-1 + NBSP
                    '\x{AD}' .                // Soft-hyphen
                    '\x{2000}-\x{200F}' .     // Various space characters