diff --git a/admin/roles/lib.php b/admin/roles/lib.php
index 68a3c8bb1c7..d2dbaba6563 100644
--- a/admin/roles/lib.php
+++ b/admin/roles/lib.php
@@ -1044,10 +1044,9 @@ class potential_assignees_below_course extends role_assign_user_selector_base {
         $sql   = " FROM {user} u
                   WHERE u.id IN ($enrolsql) $wherecondition
                         AND u.id NOT IN (
-                           SELECT u.id
-                             FROM {role_assignments} r, {user} u
+                           SELECT r.userid
+                             FROM {role_assignments} r
                             WHERE r.contextid = :contextid
-                                  AND u.id = r.userid
                                   AND r.roleid = :roleid)";
         $order = ' ORDER BY lastname ASC, firstname ASC';
 
@@ -1096,10 +1095,9 @@ class potential_assignees_course_and_above extends role_assign_user_selector_bas
         $sql = " FROM {user}
                 WHERE $wherecondition
                       AND id NOT IN (
-                         SELECT u.id
-                           FROM {role_assignments} r, {user} u
+                         SELECT r.userid
+                           FROM {role_assignments} r
                           WHERE r.contextid = :contextid
-                                AND u.id = r.userid
                                 AND r.roleid = :roleid)";
         $order = ' ORDER BY lastname ASC, firstname ASC';
 
diff --git a/user/selector/lib.php b/user/selector/lib.php
index 9dd55f63004..b2aa1c42b71 100644
--- a/user/selector/lib.php
+++ b/user/selector/lib.php
@@ -369,13 +369,13 @@ abstract class user_selector_base {
         // See if we got anything.
         if ($this->multiselect) {
             $userids = optional_param_array($this->name, array(), PARAM_INTEGER);
-        } else {
-            $userid = optional_param($this->name, 0, PARAM_INTEGER);
-            if (empty($userid)) {
-                return array();
-            }
+        } else if ($userid = optional_param($this->name, 0, PARAM_INTEGER)) {
             $userids = array($userid);
         }
+        // If there are no users there is nobody to load
+        if (empty($userids)) {
+            return array();
+        }
 
         // If we did, use the find_users method to validate the ids.
         $this->validatinguserids = $userids;