diff --git a/lib/db/upgrade.php b/lib/db/upgrade.php
index 27732f79a4e..86dac0986fb 100644
--- a/lib/db/upgrade.php
+++ b/lib/db/upgrade.php
@@ -3090,5 +3090,22 @@ function xmldb_main_upgrade($oldversion) {
         upgrade_main_savepoint(true, 2018120305.04);
     }
 
+    if ($oldversion < 2018120305.11) {
+        // Delete "orphaned" subscriptions.
+        $sql = "SELECT DISTINCT es.userid
+                  FROM {event_subscriptions} es
+             LEFT JOIN {user} u ON u.id = es.userid
+                 WHERE u.deleted = 1 OR u.id IS NULL";
+        $deletedusers = $DB->get_field_sql($sql);
+        if ($deletedusers) {
+            list($sql, $params) = $DB->get_in_or_equal($deletedusers);
+
+            // Delete orphaned subscriptions.
+            $DB->execute("DELETE FROM {event_subscriptions} WHERE userid " . $sql, $params);
+        }
+
+        upgrade_main_savepoint(true, 2018120305.11);
+    }
+
     return true;
 }
diff --git a/version.php b/version.php
index 37f6323f48a..25a31b5efc2 100644
--- a/version.php
+++ b/version.php
@@ -29,7 +29,7 @@
 
 defined('MOODLE_INTERNAL') || die();
 
-$version  = 2018120305.10;              // 20181203      = branching date YYYYMMDD - do not modify!
+$version  = 2018120305.11;              // 20181203      = branching date YYYYMMDD - do not modify!
                                         //         RR    = release increments - 00 in DEV branches.
                                         //           .XX = incremental changes.