diff --git a/lib/accesslib.php b/lib/accesslib.php
index 51675e9a363..b60be06abc5 100644
--- a/lib/accesslib.php
+++ b/lib/accesslib.php
@@ -4232,7 +4232,7 @@ function count_role_users($roleid, context $context, $parent = false) {
 
     array_unshift($params, $context->id);
 
-    $sql = "SELECT COUNT(u.id)
+    $sql = "SELECT COUNT(DISTINCT u.id)
               FROM {role_assignments} r
               JOIN {user} u ON u.id = r.userid
              WHERE (r.contextid = ? $parentcontexts)