diff --git a/mod/forum/lib.php b/mod/forum/lib.php
index e97ad191c28..bfd1218b09e 100644
--- a/mod/forum/lib.php
+++ b/mod/forum/lib.php
@@ -8331,22 +8331,28 @@ function mod_forum_core_calendar_event_action_shows_item_count(calendar_event $e
  *
  * @param calendar_event $event
  * @param \core_calendar\action_factory $factory
+ * @param int $userid User id to use for all capability checks, etc. Set to 0 for current user (default).
  * @return \core_calendar\local\event\entities\action_interface|null
  */
 function mod_forum_core_calendar_provide_event_action(calendar_event $event,
-                                                       \core_calendar\action_factory $factory) {
+                                                      \core_calendar\action_factory $factory,
+                                                      int $userid = 0) {
     global $DB, $USER;
 
-    $cm = get_fast_modinfo($event->courseid)->instances['forum'][$event->instance];
+    if (!$userid) {
+        $userid = $USER->id;
+    }
+
+    $cm = get_fast_modinfo($event->courseid, $userid)->instances['forum'][$event->instance];
     $context = context_module::instance($cm->id);
 
-    if (!has_capability('mod/forum:viewdiscussion', $context)) {
+    if (!has_capability('mod/forum:viewdiscussion', $context, $userid)) {
         return null;
     }
 
     $completion = new \completion_info($cm->get_course());
 
-    $completiondata = $completion->get_data($cm, false);
+    $completiondata = $completion->get_data($cm, false, $userid);
 
     if ($completiondata->completionstate != COMPLETION_INCOMPLETE) {
         return null;
@@ -8363,10 +8369,10 @@ function mod_forum_core_calendar_provide_event_action(calendar_event $event,
                     INNER JOIN {forum_discussions} fd ON fp.discussion=fd.id
                  WHERE
                     fp.userid=:userid AND fd.forum=:forumid";
-    $postcountparams = array('userid' => $USER->id, 'forumid' => $forum->id);
+    $postcountparams = array('userid' => $userid, 'forumid' => $forum->id);
 
     if ($forum->completiondiscussions) {
-        $count = $DB->count_records('forum_discussions', array('forum' => $forum->id, 'userid' => $USER->id));
+        $count = $DB->count_records('forum_discussions', array('forum' => $forum->id, 'userid' => $userid));
         $itemcount += ($forum->completiondiscussions >= $count) ? ($forum->completiondiscussions - $count) : 0;
     }
 
diff --git a/mod/forum/tests/lib_test.php b/mod/forum/tests/lib_test.php
index 5aee4dca258..2496b786af0 100644
--- a/mod/forum/tests/lib_test.php
+++ b/mod/forum/tests/lib_test.php
@@ -3350,6 +3350,44 @@ class mod_forum_lib_testcase extends advanced_testcase {
         $this->assertTrue($actionevent->is_actionable());
     }
 
+    public function test_forum_core_calendar_provide_event_action_for_user() {
+        global $CFG;
+
+        $this->resetAfterTest();
+        $this->setAdminUser();
+
+        // Create a course.
+        $course = $this->getDataGenerator()->create_course();
+
+        // Create a student.
+        $student = $this->getDataGenerator()->create_and_enrol($course, 'student');
+
+        // Create the activity.
+        $forum = $this->getDataGenerator()->create_module('forum', array('course' => $course->id,
+                'completionreplies' => 5, 'completiondiscussions' => 2));
+
+        // Create a calendar event.
+        $event = $this->create_action_event($course->id, $forum->id,
+                \core_completion\api::COMPLETION_EVENT_TYPE_DATE_COMPLETION_EXPECTED);
+
+        // Now log out.
+        $CFG->forcelogin = true; // We don't want to be logged in as guest, as guest users might still have some capabilities.
+        $this->setUser();
+
+        // Create an action factory.
+        $factory = new \core_calendar\action_factory();
+
+        // Decorate action event for the student.
+        $actionevent = mod_forum_core_calendar_provide_event_action($event, $factory, $student->id);
+
+        // Confirm the event was decorated.
+        $this->assertInstanceOf('\core_calendar\local\event\value_objects\action', $actionevent);
+        $this->assertEquals(get_string('view'), $actionevent->get_name());
+        $this->assertInstanceOf('moodle_url', $actionevent->get_url());
+        $this->assertEquals(7, $actionevent->get_item_count());
+        $this->assertTrue($actionevent->is_actionable());
+    }
+
     public function test_forum_core_calendar_provide_event_action_as_non_user() {
         global $CFG;
 
@@ -3412,6 +3450,45 @@ class mod_forum_lib_testcase extends advanced_testcase {
         $this->assertNull($actionevent);
     }
 
+    public function test_forum_core_calendar_provide_event_action_already_completed_for_user() {
+        global $CFG;
+
+        $this->resetAfterTest();
+        $this->setAdminUser();
+
+        $CFG->enablecompletion = 1;
+
+        // Create a course.
+        $course = $this->getDataGenerator()->create_course(array('enablecompletion' => 1));
+
+        // Create a student.
+        $student = $this->getDataGenerator()->create_and_enrol($course, 'student');
+
+        // Create the activity.
+        $forum = $this->getDataGenerator()->create_module('forum', array('course' => $course->id),
+            array('completion' => 2, 'completionview' => 1, 'completionexpected' => time() + DAYSECS));
+
+        // Get some additional data.
+        $cm = get_coursemodule_from_instance('forum', $forum->id);
+
+        // Create a calendar event.
+        $event = $this->create_action_event($course->id, $forum->id,
+            \core_completion\api::COMPLETION_EVENT_TYPE_DATE_COMPLETION_EXPECTED);
+
+        // Mark the activity as completed for the student.
+        $completion = new completion_info($course);
+        $completion->set_module_viewed($cm, $student->id);
+
+        // Create an action factory.
+        $factory = new \core_calendar\action_factory();
+
+        // Decorate action event.
+        $actionevent = mod_forum_core_calendar_provide_event_action($event, $factory, $student->id);
+
+        // Ensure result was null.
+        $this->assertNull($actionevent);
+    }
+
     public function test_mod_forum_get_tagged_posts() {
         global $DB;