diff --git a/mod/forum/db/caches.php b/mod/forum/db/caches.php
new file mode 100644
index 00000000000..ecfd9e38503
--- /dev/null
+++ b/mod/forum/db/caches.php
@@ -0,0 +1,35 @@
+<?php
+// This file is part of Moodle - https://moodle.org/
+//
+// Moodle is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// Moodle is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with Moodle.  If not, see <http://www.gnu.org/licenses/>.
+
+/**
+ * Defined caches used internally by the plugin.
+ *
+ * @package     mod_forum
+ * @category    cache
+ * @copyright   2019 Ryan Wyllie <ryan@moodle.com>
+ * @license     http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
+ */
+
+defined('MOODLE_INTERNAL') || die();
+
+$definitions = [
+    'forum_is_tracked' => [
+        'mode' => cache_store::MODE_REQUEST,
+        'simplekeys' => true,
+        'simpledata' => true,
+        'staticacceleration' => true
+    ],
+];
diff --git a/mod/forum/lang/en/forum.php b/mod/forum/lang/en/forum.php
index cfb0cd9c5c6..c376f02fb9d 100644
--- a/mod/forum/lang/en/forum.php
+++ b/mod/forum/lang/en/forum.php
@@ -50,6 +50,7 @@ $string['blockperiod_help'] = 'Students can be blocked from posting more than a
 $string['blockperioddisabled'] = 'Don\'t block';
 $string['blogforum'] = 'Standard forum displayed in a blog-like format';
 $string['bynameondate'] = 'by {$a->name} - {$a->date}';
+$string['cachedef_forum_is_tracked'] = 'Forum tracking status for user';
 $string['cannotadd'] = 'Could not add the discussion for this forum';
 $string['cannotadddiscussion'] = 'Adding discussions to this forum requires group membership.';
 $string['cannotadddiscussionall'] = 'You do not have permission to add a new discussion topic for all participants.';
diff --git a/mod/forum/lib.php b/mod/forum/lib.php
index 80c06f28719..d9f9748f5e7 100644
--- a/mod/forum/lib.php
+++ b/mod/forum/lib.php
@@ -5970,6 +5970,13 @@ function forum_tp_is_tracked($forum, $user=false) {
         return false;
     }
 
+    $cache = cache::make('mod_forum', 'forum_is_tracked');
+    $forumid = is_numeric($forum) ? $forum : $forum->id;
+    $key = $forumid . '_' . $user->id;
+    if ($cachedvalue = $cache->get($key)) {
+        return $cachedvalue == 'tracked';
+    }
+
     // Work toward always passing an object...
     if (is_numeric($forum)) {
         debugging('Better use proper forum object.', DEBUG_DEVELOPER);
@@ -5985,10 +5992,17 @@ function forum_tp_is_tracked($forum, $user=false) {
     $userpref = $DB->get_record('forum_track_prefs', array('userid' => $user->id, 'forumid' => $forum->id));
 
     if ($CFG->forum_allowforcedreadtracking) {
-        return $forumforced || ($forumallows && $userpref === false);
+        $istracked = $forumforced || ($forumallows && $userpref === false);
     } else {
-        return  ($forumallows || $forumforced) && $userpref === false;
+        $istracked = ($forumallows || $forumforced) && $userpref === false;
     }
+
+    // We have to store a string here because the cache API returns false
+    // when it can't find the key which would be confused with our legitimate
+    // false value. *sigh*.
+    $cache->set($key, $istracked ? 'tracked' : 'not');
+
+    return $istracked;
 }
 
 /**
diff --git a/mod/forum/tests/lib_test.php b/mod/forum/tests/lib_test.php
index 6bf04eeac49..eebed2c1386 100644
--- a/mod/forum/tests/lib_test.php
+++ b/mod/forum/tests/lib_test.php
@@ -271,6 +271,7 @@ class mod_forum_lib_testcase extends advanced_testcase {
 
         $this->resetAfterTest();
 
+        $cache = cache::make('mod_forum', 'forum_is_tracked');
         $useron = $this->getDataGenerator()->create_user(array('trackforums' => 1));
         $useroff = $this->getDataGenerator()->create_user(array('trackforums' => 0));
         $course = $this->getDataGenerator()->create_course();
@@ -310,6 +311,7 @@ class mod_forum_lib_testcase extends advanced_testcase {
         $result = forum_tp_is_tracked($forumoptional, $useroff);
         $this->assertEquals(false, $result);
 
+        $cache->purge();
         // Don't allow force.
         $CFG->forum_allowforcedreadtracking = 0;
 
@@ -343,6 +345,7 @@ class mod_forum_lib_testcase extends advanced_testcase {
         forum_tp_stop_tracking($forumforce->id, $useroff->id);
         forum_tp_stop_tracking($forumoptional->id, $useroff->id);
 
+        $cache->purge();
         // Allow force.
         $CFG->forum_allowforcedreadtracking = 1;
 
@@ -362,6 +365,7 @@ class mod_forum_lib_testcase extends advanced_testcase {
         $result = forum_tp_is_tracked($forumoptional, $useroff);
         $this->assertEquals(false, $result);
 
+        $cache->purge();
         // Don't allow force.
         $CFG->forum_allowforcedreadtracking = 0;