diff --git a/completion/classes/manager.php b/completion/classes/manager.php
index 67c0f0c52a5..25a86f27c4a 100644
--- a/completion/classes/manager.php
+++ b/completion/classes/manager.php
@@ -528,7 +528,7 @@ class manager {
             $data['customrules'] = $customdata ? json_encode($customdata) : null;
             $defaults['customrules'] = null;
         }
-        $data = array_intersect_key($data, $defaults);
+        $data = array_merge($defaults, $data);
 
         // Get names of the affected modules.
         list($modidssql, $params) = $DB->get_in_or_equal($modids);
diff --git a/completion/tests/behat/default_activity_completion.feature b/completion/tests/behat/default_activity_completion.feature
index 74896286e0b..892fbb23214 100644
--- a/completion/tests/behat/default_activity_completion.feature
+++ b/completion/tests/behat/default_activity_completion.feature
@@ -29,13 +29,19 @@ Feature: Allow teachers to edit the default activity completion rules in a cours
     And I set the field "Course completion tertiary navigation" to "Default activity completion"
     And I click on "Expand Assignment" "button"
     And I set the following fields to these values:
-      | Add requirements         | 1                  |
-      | completionview_assign     | 0                                                 |
-      | completionusegrade_assign | 1                                                 |
-      | completionsubmit_assign   | 1                                                 |
+      | Add requirements          | 1 |
+      | completionview_assign     | 1 |
+      | completionusegrade_assign | 1 |
+      | completionsubmit_assign   | 1 |
     And I should not see "Cancel" in the "[data-region='activitycompletion-forum']" "css_element"
     And I click on "Save changes" "button" in the "[data-region='activitycompletion-assign']" "css_element"
     Then I should see "Changes saved"
+    And I navigate to "Course completion" in current page administration
+    And I set the field "Course completion tertiary navigation" to "Default activity completion"
+    And I click on "Expand Assignment" "button"
+    And I set the following fields to these values:
+      | completionview_assign     | 0 |
+    And I click on "Save changes" "button" in the "[data-region='activitycompletion-assign']" "css_element"
     And I am on "Course 1" course homepage with editing mode on
     And I press "Add an activity or resource"
     And I click on "Add a new Assignment" "link" in the "Add an activity or resource" "dialogue"