=== modified file 'install.php'
--- install.php	2006-11-26 02:19:59 +0000
+++ install.php	2006-12-16 06:12:24 +0000
@@ -309,8 +309,8 @@ function _install_settings_form_validate
   }
 
   // Verify the table prefix
-  if (!empty($db_prefix) && is_string($db_prefix) && preg_match('/[^A-Za-z0-9_]/', $db_prefix)) {
-    form_set_error('db_prefix', st('The database table prefix you have entered, %db_prefix, is invalid. The table prefix can only contain alphanumeric characters and underscores.', array('%db_prefix' => $db_prefix)), 'error');
+  if (!empty($db_prefix) && is_string($db_prefix) && !preg_match('/^[A-Za-z0-9_]+(\.[A-Za-z0-9]*)?$/', $db_prefix)) {
+    form_set_error('db_prefix', st('The database table prefix you have entered, %db_prefix, is invalid. The table prefix can only contain alphanumeric characters and underscores and optionally one dot in the middle.', array('%db_prefix' => $db_prefix)), 'error');
   }
 
   if (!empty($db_port) && !is_numeric($db_port)) {