Index: src/wp-admin/includes/schema.php
===================================================================
--- src/wp-admin/includes/schema.php	(revision 36633)
+++ src/wp-admin/includes/schema.php	(working copy)
@@ -204,7 +204,8 @@
   display_name varchar(250) NOT NULL default '',
   PRIMARY KEY  (ID),
   KEY user_login_key (user_login),
-  KEY user_nicename (user_nicename)
+  KEY user_nicename (user_nicename),
+  KEY user_email (user_email)
 ) $charset_collate;\n";
 
 	// Multisite users table
@@ -223,7 +224,8 @@
   deleted tinyint(2) NOT NULL default '0',
   PRIMARY KEY  (ID),
   KEY user_login_key (user_login),
-  KEY user_nicename (user_nicename)
+  KEY user_nicename (user_nicename),
+  KEY user_email (user_email)
 ) $charset_collate;\n";
 
 	// Usermeta.