diff --git a/lib/modinfolib.php b/lib/modinfolib.php
index f9994fee7ef53..c2fc0d025b3ba 100644
--- a/lib/modinfolib.php
+++ b/lib/modinfolib.php
@@ -1074,6 +1074,8 @@ function get_fast_modinfo(&$course, $userid=0) {
     if (count($cache) > MAX_MODINFO_CACHE_SIZE) {
         reset($cache);
         $key = key($cache);
+        unset($cache[$key]->instances);
+        unset($cache[$key]->cms);
         unset($cache[$key]);
     }