diff --git a/mod/glossary/classes/local/concept_cache.php b/mod/glossary/classes/local/concept_cache.php
index a7f42b9be5a..cd5adc8046b 100644
--- a/mod/glossary/classes/local/concept_cache.php
+++ b/mod/glossary/classes/local/concept_cache.php
@@ -159,6 +159,14 @@ class concept_cache {
 
         $courseid = (int)$courseid;
 
+        // Get info on any glossaries in this course.
+        $modinfo = get_fast_modinfo($courseid);
+        $cminfos = $modinfo->get_instances_of('glossary');
+        if (!$cminfos) {
+            // No glossaries in this course, so don't do any work.
+            return array(array(), array());
+        }
+
         $cache = \cache::make('mod_glossary', 'concepts');
         $data = $cache->get($courseid);
         if (is_array($data)) {
@@ -201,8 +209,6 @@ class concept_cache {
         $concepts = $allconcepts;
 
         // Verify access control to glossary instances.
-        $modinfo = get_fast_modinfo($courseid);
-        $cminfos = $modinfo->get_instances_of('glossary');
         foreach ($concepts as $modid => $unused) {
             if (!isset($cminfos[$modid])) {
                 // This should not happen.