diff --git a/mod/assign/backup/moodle2/backup_assign_stepslib.php b/mod/assign/backup/moodle2/backup_assign_stepslib.php
index 4facb4fda31..0f018ca9212 100644
--- a/mod/assign/backup/moodle2/backup_assign_stepslib.php
+++ b/mod/assign/backup/moodle2/backup_assign_stepslib.php
@@ -61,6 +61,7 @@ class backup_assign_activity_structure_step extends backup_activity_structure_st
 
         // To know if we are including userinfo.
         $userinfo = $this->get_setting_value('userinfo');
+        $groupinfo = $this->get_setting_value('groups');
 
         // Define each element separated.
         $assign = new backup_nested_element('assign', array('id'),
@@ -159,8 +160,12 @@ class backup_assign_activity_structure_step extends backup_activity_structure_st
             $userflag->set_source_table('assign_user_flags',
                                      array('assignment' => backup::VAR_PARENTID));
 
-            $submission->set_source_table('assign_submission',
-                                     array('assignment' => backup::VAR_PARENTID));
+            $submissionparams = array('assignment' => backup::VAR_PARENTID);
+            if (!$groupinfo) {
+                // Without group info, skip group submissions.
+                $submissionparams['groupid'] = backup_helper::is_sqlparam(0);
+            }
+            $submission->set_source_table('assign_submission', $submissionparams);
 
             $grade->set_source_table('assign_grades',
                                      array('assignment' => backup::VAR_PARENTID));
@@ -172,6 +177,10 @@ class backup_assign_activity_structure_step extends backup_activity_structure_st
             $overrideparams['userid'] = backup_helper::is_sqlparam(null); // Without userinfo, skip user overrides.
         }
 
+        if (!$groupinfo) {
+            // Without group info, skip group overrides.
+            $overrideparams['groupid'] = backup_helper::is_sqlparam(0);
+        }
         $override->set_source_table('assign_overrides', $overrideparams);
 
         // Define id annotations.
diff --git a/mod/assign/backup/moodle2/restore_assign_stepslib.php b/mod/assign/backup/moodle2/restore_assign_stepslib.php
index 0987c53e531..d4ba0a56a18 100644
--- a/mod/assign/backup/moodle2/restore_assign_stepslib.php
+++ b/mod/assign/backup/moodle2/restore_assign_stepslib.php
@@ -387,6 +387,12 @@ class restore_assign_activity_structure_step extends restore_activity_structure_
             return;
         }
 
+        // Skip group overrides if we are not restoring groupinfo.
+        $groupinfo = $this->get_setting_value('groups');
+        if (!$groupinfo && !is_null($data->groupid)) {
+            return;
+        }
+
         $data->assignid = $this->get_new_parentid('assign');
 
         if (!is_null($data->userid)) {
diff --git a/mod/assign/lib.php b/mod/assign/lib.php
index 002404dd379..ee787849bc4 100644
--- a/mod/assign/lib.php
+++ b/mod/assign/lib.php
@@ -258,8 +258,11 @@ function assign_update_events($assign, $override = null) {
         // Only load events for this override.
         if (isset($override->userid)) {
             $conds['userid'] = $override->userid;
-        } else {
+        } else if (isset($override->groupid)) {
             $conds['groupid'] = $override->groupid;
+        } else {
+            // This is not a valid override, it may have been left from a bad import or restore.
+            $conds['groupid'] = $conds['userid'] = 0;
         }
     }
     $oldevents = $DB->get_records('event', $conds, 'id ASC');
diff --git a/mod/assign/tests/lib_test.php b/mod/assign/tests/lib_test.php
index 4d47f855a94..54054b3f256 100644
--- a/mod/assign/tests/lib_test.php
+++ b/mod/assign/tests/lib_test.php
@@ -362,14 +362,23 @@ class mod_assign_lib_testcase extends advanced_testcase {
             ]);
 
         $instance = $assign->get_instance();
-        $eventparams = ['modulename' => 'assign', 'instance' => $instance->id];
+        $eventparams = [
+            'modulename' => 'assign',
+            'instance' => $instance->id,
+            'eventtype' => ASSIGN_EVENT_TYPE_DUE,
+            'groupid' => 0
+        ];
 
         // Make sure the calendar event for assignment 1 matches the initial due date.
         $eventtime = $DB->get_field('event', 'timestart', $eventparams, MUST_EXIST);
         $this->assertEquals($eventtime, $duedate);
 
         // Manually update assignment 1's due date.
-        $DB->update_record('assign', (object) ['id' => $instance->id, 'duedate' => $newduedate]);
+        $DB->update_record('assign', (object) [
+            'id' => $instance->id,
+            'duedate' => $newduedate,
+            'course' => $course->id
+        ]);
 
         // Then refresh the assignment events of assignment 1's course.
         $this->assertTrue(assign_refresh_events($course->id));
@@ -380,15 +389,25 @@ class mod_assign_lib_testcase extends advanced_testcase {
 
         // Create a second course and assignment.
         $othercourse = $this->getDataGenerator()->create_course();;
-        $otherassign = $this->create_instance($othercourse, ['duedate' => $duedate, 'course' => $othercourse->id]);
+        $otherassign = $this->create_instance($othercourse, [
+            'duedate' => $duedate,
+        ]);
         $otherinstance = $otherassign->get_instance();
 
         // Manually update assignment 1 and 2's due dates.
         $newduedate += DAYSECS;
-        $DB->update_record('assign', (object)['id' => $instance->id, 'duedate' => $newduedate]);
-        $DB->update_record('assign', (object)['id' => $otherinstance->id, 'duedate' => $newduedate]);
+        $DB->update_record('assign', (object)[
+            'id' => $instance->id,
+            'duedate' => $newduedate,
+            'course' => $course->id
+        ]);
+        $DB->update_record('assign', (object)[
+            'id' => $otherinstance->id,
+            'duedate' => $newduedate,
+            'course' => $othercourse->id
+        ]);
 
-        // Refresh events of all courses.
+        // Refresh events of all courses and check the calendar events matches the new date.
         $this->assertTrue(assign_refresh_events());
 
         // Check the due date calendar event for assignment 1.