Index: wp-admin/upgrade-schema.php
===================================================================
--- wp-admin/upgrade-schema.php	(revision 3754)
+++ wp-admin/upgrade-schema.php	(working copy)
@@ -73,7 +73,7 @@
   option_admin_level int(11) NOT NULL default '1',
   autoload enum('yes','no') NOT NULL default 'yes',
   PRIMARY KEY  (option_id,blog_id,option_name),
-  KEY option_name (option_name)
+  UNIQUE option_name (option_name)
 );
 CREATE TABLE $wpdb->post2cat (
   rel_id bigint(20) NOT NULL auto_increment,