diff --git multiple_email.install multiple_email.install
index 22b15e3..5a5eb3a 100644
--- multiple_email.install
+++ multiple_email.install
@@ -23,7 +23,8 @@ function multiple_email_install() {
       1
     FROM {users}
     WHERE uid != 0
-    ON DUPLICATE KEY UPDATE email=email
+    AND mail != ''
+    GROUP BY mail
   ");
 }