diff --git a/lib/behat/form_field/behat_form_date.php b/lib/behat/form_field/behat_form_date.php
index 010b5aaffc8..030d8525992 100644
--- a/lib/behat/form_field/behat_form_date.php
+++ b/lib/behat/form_field/behat_form_date.php
@@ -56,6 +56,14 @@ class behat_form_date extends behat_form_group {
             // Disable the given date selector field.
             $this->set_child_field_value('enabled', false);
         } else if (is_numeric($value)) { // The value is numeric (unix timestamp).
+            // First, reset the day always to an existing one (1st). Without that
+            // undesired modifications (JS) happens when changing of month and day if
+            // the interim combination doesn't exists (for example, 31 March => 01 April).
+            // Note that instead of always setting the day to 1, this could be a little more
+            // clever, for example only changing when the day > 28, or only when the
+            // months (current or changed) have less days that the other. But that would
+            // require more complex calculations than the simpler line below.
+            $this->set_child_field_value('day', 1);
             // Assign the mapped values to each form element in the date selector field.
             foreach ($this->get_mapped_fields($value) as $childname => $childvalue) {
                 $this->set_child_field_value($childname, $childvalue);
@@ -74,11 +82,18 @@ class behat_form_date extends behat_form_group {
      * @return array
      */
     protected function get_mapped_fields(int $timestamp): array {
+        // Order is important, first enable, and then year -> month -> day
+        // (other order can lead to some transitions not working as expected,
+        // for example, changing from 15 June to 31 August, Behat ends with
+        // date being 1 August if the modification order is day, then month).
+        // Note that the behaviour described above is 100% reproducible
+        // manually, with the form (JS) auto-fixing things in the middle and
+        // leading to undesired final dates.
         return [
             'enabled' => true,
-            'day' => date('j', $timestamp),
-            'month' => date('n', $timestamp),
             'year' => date('Y', $timestamp),
+            'month' => date('n', $timestamp),
+            'day' => date('j', $timestamp),
         ];
     }
 
diff --git a/lib/tests/behat/datetime_any.feature b/lib/tests/behat/datetime_any.feature
new file mode 100644
index 00000000000..cb18187d13b
--- /dev/null
+++ b/lib/tests/behat/datetime_any.feature
@@ -0,0 +1,33 @@
+@core @javascript @core_form
+Feature: Any day / month / year combination in date form elements works ok.
+  In order to use date / datetime elements with Behat
+  as a user
+  Any day / month / year combination must work ok
+
+  @javascript
+  Scenario Outline: Verify that setting any date / datetime is possible
+    Given the following "courses" exist:
+      | fullname | shortname | format |
+      | Course 1 | C1        | topics |
+    And the following "activity" exist:
+      | activity   | name          | intro                              | course | idnumber |
+      | assign     | Assignment 01 | Assign activity to test some dates | C1     | assign01 |
+    Given I am on the "C1" "Course" page logged in as "admin"
+    And I follow "Assignment 01"
+    And I navigate to "Edit settings" in current page administration
+    And I expand all fieldsets
+    And I set the field "Due date" to "<initial_date>"
+    And I set the field "Due date" to "<final_date>"
+    When I press "Save and display"
+    Then I should see "<date_result>" in the "Due date" "table_row"
+
+    Examples:
+      | initial_date | final_date   | date_result                       | case_explanation (times Australia/Perth)   |
+      | ##now##      | ##tomorrow## | ##tomorrow##%A, %d %B %Y, %I:%M## | change of day, any day, back and forth     |
+      | ##tomorrow## | ##now##      | ##now##%A, %d %B %Y, %I:%M##      |                                            |
+      | 1617256800   | 1617170400   | Wednesday, 31 March 2021, 2:00    | change of month, back and forth            |
+      | 1617170400   | 1617256800   | Thursday, 1 April 2021, 2:00      |                                            |
+      | 1740808800   | 1709186400   | Thursday, 29 February 2024, 2:00  | change of month, leap year, back and forth |
+      | 1709186400   | 1740808800   | Saturday, 1 March 2025, 2:00      |                                            |
+      | 1577858400   | 1577772000   | Tuesday, 31 December 2019, 2:00   | change of year, back and forth             |
+      | 1577772000   | 1577858400   | Wednesday, 1 January 2020, 2:00   |                                            |