diff --git a/addons/mail/mail_thread.py b/addons/mail/mail_thread.py
index 3b0d97c8240..8dcc39163ec 100644
--- a/addons/mail/mail_thread.py
+++ b/addons/mail/mail_thread.py
@@ -1470,6 +1470,7 @@ class mail_thread(osv.AbstractModel):
             :param boolean check_followers: check in document followers
         """
         partner_obj = self.pool['res.partner']
+        users_obj = self.pool['res.users']
         partner_ids = []
         obj = None
         if id and (model or self._name != 'mail.thread') and check_followers:
@@ -1495,16 +1496,15 @@ class mail_thread(osv.AbstractModel):
             email_brackets = "<%s>" % email_address
             if not partner_id:
                 # exact, case-insensitive match
-                ids = partner_obj.search(cr, SUPERUSER_ID,
-                                         [('email', '=ilike', email_address),
-                                          ('user_ids', '!=', False)],
+                user_ids = users_obj.search(cr, SUPERUSER_ID,
+                                         [('email', '=ilike', email_address)],
                                          limit=1, context=context)
+                ids = [users_obj.browse(cr, SUPERUSER_ID, user_ids, context=context).partner_id.id]
                 if not ids:
                     # if no match with addr-spec, attempt substring match within name-addr pair
-                    ids = partner_obj.search(cr, SUPERUSER_ID,
-                                             [('email', 'ilike', email_brackets),
-                                              ('user_ids', '!=', False)],
-                                             limit=1, context=context)
+                    user_ids = users_obj.search(cr, SUPERUSER_ID,
+                                             [('email', 'ilike', email_brackets)], limit=1, context=context)
+                    ids = [users_obj.browse(cr, SUPERUSER_ID, user_ids, context=context).partner_id.id]
                 if ids:
                     partner_id = ids[0]
             # third try: check in partners