diff --git a/mod/forum/externallib.php b/mod/forum/externallib.php
index 9b3daffcb5e..b3ab20ec4fc 100644
--- a/mod/forum/externallib.php
+++ b/mod/forum/externallib.php
@@ -689,7 +689,7 @@ class mod_forum_external extends external_api {
      * @throws moodle_exception
      */
     public static function view_forum_discussion($discussionid) {
-        global $DB, $CFG;
+        global $DB, $CFG, $USER;
         require_once($CFG->dirroot . "/mod/forum/lib.php");
 
         $params = self::validate_parameters(self::view_forum_discussion_parameters(),
@@ -711,6 +711,11 @@ class mod_forum_external extends external_api {
         // Call the forum/lib API.
         forum_discussion_view($modcontext, $forum, $discussion);
 
+        // Mark as read if required.
+        if (!$CFG->forum_usermarksread && forum_tp_is_tracked($forum)) {
+            forum_tp_mark_discussion_read($USER, $discussion->id);
+        }
+
         $result = array();
         $result['status'] = true;
         $result['warnings'] = $warnings;
diff --git a/mod/forum/tests/externallib_test.php b/mod/forum/tests/externallib_test.php
index 455abcaa5ee..30b8ff8a943 100644
--- a/mod/forum/tests/externallib_test.php
+++ b/mod/forum/tests/externallib_test.php
@@ -204,6 +204,12 @@ class mod_forum_external_testcase extends externallib_advanced_testcase {
         $forum1 = self::getDataGenerator()->create_module('forum', $record);
         $forum1context = context_module::instance($forum1->cmid);
 
+        // Forum with tracking enabled.
+        $record = new stdClass();
+        $record->course = $course1->id;
+        $forum2 = self::getDataGenerator()->create_module('forum', $record);
+        $forum2context = context_module::instance($forum2->cmid);
+
         // Add discussions to the forums.
         $record = new stdClass();
         $record->course = $course1->id;
@@ -217,6 +223,12 @@ class mod_forum_external_testcase extends externallib_advanced_testcase {
         $record->forum = $forum1->id;
         $discussion2 = self::getDataGenerator()->get_plugin_generator('mod_forum')->create_discussion($record);
 
+        $record = new stdClass();
+        $record->course = $course1->id;
+        $record->userid = $user2->id;
+        $record->forum = $forum2->id;
+        $discussion3 = self::getDataGenerator()->get_plugin_generator('mod_forum')->create_discussion($record);
+
         // Add 2 replies to the discussion 1 from different users.
         $record = new stdClass();
         $record->discussion = $discussion1->id;
@@ -314,6 +326,31 @@ class mod_forum_external_testcase extends externallib_advanced_testcase {
         $posts = external_api::clean_returnvalue(mod_forum_external::get_forum_discussion_posts_returns(), $posts);
         $this->assertEquals(1, count($posts['posts']));
 
+        // Test discussion tracking on not tracked forum.
+        $result = mod_forum_external::view_forum_discussion($discussion1->id);
+        $result = external_api::clean_returnvalue(mod_forum_external::view_forum_discussion_returns(), $result);
+        $this->assertTrue($result['status']);
+        $this->assertEmpty($result['warnings']);
+
+        // Test posts have not been marked as read.
+        $posts = mod_forum_external::get_forum_discussion_posts($discussion1->id, 'modified', 'DESC');
+        $posts = external_api::clean_returnvalue(mod_forum_external::get_forum_discussion_posts_returns(), $posts);
+        foreach ($posts['posts'] as $post) {
+            $this->assertFalse($post['postread']);
+        }
+
+        // Test discussion tracking on tracked forum.
+        $result = mod_forum_external::view_forum_discussion($discussion3->id);
+        $result = external_api::clean_returnvalue(mod_forum_external::view_forum_discussion_returns(), $result);
+        $this->assertTrue($result['status']);
+        $this->assertEmpty($result['warnings']);
+
+        // Test posts have been marked as read.
+        $posts = mod_forum_external::get_forum_discussion_posts($discussion3->id, 'modified', 'DESC');
+        $posts = external_api::clean_returnvalue(mod_forum_external::get_forum_discussion_posts_returns(), $posts);
+        foreach ($posts['posts'] as $post) {
+            $this->assertTrue($post['postread']);
+        }
     }
 
     /**