diff --git a/auth/db/auth.php b/auth/db/auth.php
index a355a7fa169..76c70621bc7 100644
--- a/auth/db/auth.php
+++ b/auth/db/auth.php
@@ -307,12 +307,15 @@ class auth_plugin_db extends auth_plugin_base {
                         FROM {user} u
                        WHERE u.auth=:authtype AND u.deleted=0 AND u.mnethostid=:mnethostid $suspendselect";
                   $params['mnethostid'] = $CFG->mnet_localhost_id;
-                  $internalusers = $DB->get_records_sql($sql, $params);
-                foreach ($internalusers as $internaluser) {
-                    if (!in_array($internaluser->username, $userlist)) {
+                  $internalusersrs = $DB->get_recordset_sql($sql, $params);
+                foreach ($internalusersrs as $internaluser) {
+                    // Arrange the associative array.
+                    $usernamelist = array_flip($userlist);
+                    if (!array_key_exists($internaluser->username, $usernamelist)) {
                         $removeusers[] = $internaluser;
                     }
                 }
+                $internalusersrs->close();
             } else {
                 $sql = "SELECT u.id, u.username
                           FROM {user} u