diff --git a/CHANGELOG.md b/CHANGELOG.md
index bb036dc..ff68c4b 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -7,6 +7,10 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 
 ## [unreleased]
 
+### Fixed
+
+- Handle mandatory template fields in history button escalation
+
 ## [2.9.18] - 2025-30-09
 
 ### Fixed
diff --git a/inc/ticket.class.php b/inc/ticket.class.php
index 0aac77e..2c8e96c 100644
--- a/inc/ticket.class.php
+++ b/inc/ticket.class.php
@@ -605,24 +605,72 @@ public static function climb_group($tickets_id, $groups_id, $no_redirect = false
             'type'       => CommonITILActor::ASSIGN,
         ];
         if (!$group_ticket->find($condition)) {
-            $ticket_group = new Group_Ticket();
-            PluginEscaladeTask_Manager::setTicketTask([
-                'tickets_id' => $tickets_id,
-                'is_private' => true,
-                'state'      => Planning::INFO,
-                // Sanitize before merging with $_POST['comment'] which is already sanitized
-                'content'    => Sanitizer::sanitize(
-                    '<p><i>' . sprintf(__('Escalation to the group %s.', 'escalade'), Sanitizer::unsanitize($group->getName())) . '</i></p><hr />',
-                ),
-            ]);
+            // Get ticket to retrieve existing data for template validation
             $ticket = new Ticket();
-            $ticket->update([
+            $ticket->getFromDB($tickets_id);
+
+            // Prepare minimal update with only the fields needed to pass template validation
+            // This ensures mandatory fields from templates are satisfied while only changing the assigned group
+            $update_data = [
                 'id'           => $tickets_id,
                 '_itil_assign' => [
                     'groups_id' => $groups_id,
                     '_type'    => 'group',
                 ],
+                // Also use _groups_id_assign to satisfy mandatory field validation
+                '_groups_id_assign' => [$groups_id],
+            ];
+
+            // Add mandatory fields that are commonly required by templates
+            // to prevent "Mandatory fields are not filled" errors
+            $required_fields = ['name', 'content', 'itilcategories_id', 'urgency', 'entities_id', 'type'];
+            foreach ($required_fields as $field) {
+                if (isset($ticket->fields[$field]) && !empty($ticket->fields[$field])) {
+                    $update_data[$field] = $ticket->fields[$field];
+                }
+            }
+
+            // Add existing actors to satisfy mandatory actor fields from template
+            $ticket_user = new \Ticket_User();
+            $ticket_group_model = new \Group_Ticket();
+
+            // Get existing requesters
+            $requesters = $ticket_user->find([
+                'tickets_id' => $tickets_id,
+                'type' => CommonITILActor::REQUESTER,
             ]);
+            if (!empty($requesters)) {
+                $update_data['_users_id_requester'] = array_column($requesters, 'users_id');
+            }
+
+            // Get existing observers
+            $observers = $ticket_user->find([
+                'tickets_id' => $tickets_id,
+                'type' => CommonITILActor::OBSERVER,
+            ]);
+            if (!empty($observers)) {
+                $update_data['_users_id_observer'] = array_column($observers, 'users_id');
+            }
+
+            // Get existing requester groups
+            $requester_groups = $ticket_group_model->find([
+                'tickets_id' => $tickets_id,
+                'type' => CommonITILActor::REQUESTER,
+            ]);
+            if (!empty($requester_groups)) {
+                $update_data['_groups_id_requester'] = array_column($requester_groups, 'groups_id');
+            }
+
+            // Get existing observer groups
+            $observer_groups = $ticket_group_model->find([
+                'tickets_id' => $tickets_id,
+                'type' => CommonITILActor::OBSERVER,
+            ]);
+            if (!empty($observer_groups)) {
+                $update_data['_groups_id_observer'] = array_column($observer_groups, 'groups_id');
+            }
+
+            $ticket->update($update_data);
         }
 
         if (!$no_redirect) {
diff --git a/tests/Units/TicketTest.php b/tests/Units/TicketTest.php
index 7b1e702..6884918 100644
--- a/tests/Units/TicketTest.php
+++ b/tests/Units/TicketTest.php
@@ -1382,4 +1382,147 @@ public function testHistoryButtonEscalationWithMandatoryTemplateFields()
         $group1->delete(['id' => $group1_id], true);
         $group2->delete(['id' => $group2_id], true);
     }
+
+    /**
+     * Test that using the History button escalation works correctly with mandatory "Assigned Group" field
+     */
+    public function testHistoryButtonEscalationWithMandatoryAssignedGroupField()
+    {
+        $this->login();
+
+        // Load Escalade plugin configuration
+        $config = new PluginEscaladeConfig();
+        $conf = $config->find();
+        $conf = reset($conf);
+        $config->getFromDB($conf['id']);
+        $this->assertGreaterThan(0, $conf['id']);
+        PluginEscaladeConfig::loadInSession();
+
+        // Create a ticket template with mandatory "Assigned Group" field (field num 8)
+        $template = $this->createItem(\TicketTemplate::class, [
+            'name' => 'Test template with mandatory assigned group',
+            'entities_id' => 0,
+            'is_recursive' => 1,
+        ]);
+
+        // Add mandatory field for "Groupe de techniciens" (Assigned Group)
+        $mandatory_field = $this->createItem(\TicketTemplateMandatoryField::class, [
+            'tickettemplates_id' => $template->getID(),
+            'num' => 8, // _groups_id_assign field number
+        ]);
+
+        // Also add mandatory requester field to match real-world scenarios
+        $mandatory_field2 = $this->createItem(\TicketTemplateMandatoryField::class, [
+            'tickettemplates_id' => $template->getID(),
+            'num' => 4, // _users_id_requester field number
+        ]);
+
+        // Create a category linked to this template
+        $category = $this->createItem(\ITILCategory::class, [
+            'name' => 'Test category with mandatory assigned group',
+            'tickettemplates_id_incident' => $template->getID(),
+            'is_incident' => 1,
+            'entities_id' => 0,
+            'is_recursive' => 1,
+        ]);
+
+        // Create a requester user
+        $requester = $this->createItem(\User::class, [
+            'name' => 'requester_assigned_group_test',
+            'realname' => 'AssignedGroupTest',
+            'firstname' => 'Requester',
+        ]);
+
+        // Create first escalation group
+        $group1 = $this->createItem(\Group::class, [
+            'name' => 'First assigned group for escalation',
+            'entities_id' => 0,
+            'is_recursive' => 1,
+            'is_assign' => 1,
+        ]);
+
+        // Create second escalation group
+        $group2 = $this->createItem(\Group::class, [
+            'name' => 'Second assigned group for escalation',
+            'entities_id' => 0,
+            'is_recursive' => 1,
+            'is_assign' => 1,
+        ]);
+
+        // Create third group for history button test
+        $group3 = $this->createItem(\Group::class, [
+            'name' => 'Third assigned group for history',
+            'entities_id' => 0,
+            'is_recursive' => 1,
+            'is_assign' => 1,
+        ]);
+
+        // Create a ticket with the template, mandatory requester and mandatory assigned group filled
+        $ticket = $this->createItem(\Ticket::class, [
+            'name' => 'Test ticket with mandatory assigned group',
+            'content' => 'Content for testing mandatory assigned group in history button',
+            'itilcategories_id' => $category->getID(),
+            '_users_id_requester' => [$requester->getID()],
+            '_groups_id_assign' => [$group1->getID()],
+        ]);
+
+        // Verify initial group assignment
+        $group_ticket = new \Group_Ticket();
+        $initial_groups = $group_ticket->find([
+            'tickets_id' => $ticket->getID(),
+            'type' => CommonITILActor::ASSIGN,
+        ]);
+        $this->assertEquals(1, count($initial_groups));
+
+        // Escalate to second group
+        $this->createItem(\Group_Ticket::class, [
+            'tickets_id' => $ticket->getID(),
+            'groups_id' => $group2->getID(),
+            'type' => CommonITILActor::ASSIGN,
+        ]);
+
+        // Escalate to third group to create more history
+        $this->createItem(\Group_Ticket::class, [
+            'tickets_id' => $ticket->getID(),
+            'groups_id' => $group3->getID(),
+            'type' => CommonITILActor::ASSIGN,
+        ]);
+
+        // Now test the history button escalation using climb_group
+        // This reproduces issue #381 where mandatory "Groupe de techniciens" field causes an error
+        PluginEscaladeTicket::climb_group($ticket->getID(), $group1->getID(), true);
+
+        // Verify that no error occurred during the climb_group operation
+        // by checking that group1 is now assigned
+        $group1_assigned = $group_ticket->find([
+            'tickets_id' => $ticket->getID(),
+            'groups_id' => $group1->getID(),
+            'type' => CommonITILActor::ASSIGN,
+        ]);
+        $this->assertGreaterThan(0, count($group1_assigned), 'Group 1 should be assigned after climb_group');
+
+        // Test climbing to group2 (another history group)
+        PluginEscaladeTicket::climb_group($ticket->getID(), $group2->getID(), true);
+
+        $group2_assigned = $group_ticket->find([
+            'tickets_id' => $ticket->getID(),
+            'groups_id' => $group2->getID(),
+            'type' => CommonITILActor::ASSIGN,
+        ]);
+        $this->assertGreaterThan(0, count($group2_assigned), 'Group 2 should be assigned after second climb_group');
+
+        // Verify that the requester is still properly assigned
+        $ticket_user = new \Ticket_User();
+        $requesters_after = $ticket_user->find([
+            'tickets_id' => $ticket->getID(),
+            'type' => CommonITILActor::REQUESTER,
+        ]);
+        $this->assertEquals(1, count($requesters_after));
+        $requester_after = reset($requesters_after);
+        $this->assertEquals($requester->getID(), $requester_after['users_id']);
+
+        // Verify that the ticket still has the correct category with template
+        $ticket->getFromDB($ticket->getID());
+        $this->assertEquals($category->getID(), $ticket->fields['itilcategories_id']);
+    }
 }