diff --git a/src/Bundle/ChillThirdPartyBundle/Controller/ThirdpartyDuplicateController.php b/src/Bundle/ChillThirdPartyBundle/Controller/ThirdpartyDuplicateController.php
index 78f99e8a9..56967a9ce 100644
--- a/src/Bundle/ChillThirdPartyBundle/Controller/ThirdpartyDuplicateController.php
+++ b/src/Bundle/ChillThirdPartyBundle/Controller/ThirdpartyDuplicateController.php
@@ -14,16 +14,16 @@ namespace Chill\ThirdPartyBundle\Controller;
 use Chill\PersonBundle\Form\PersonConfimDuplicateType;
 use Chill\ThirdPartyBundle\Entity\ThirdParty;
 use Chill\ThirdPartyBundle\Form\ThirdpartyFindDuplicateType;
-use Chill\ThirdPartyBundle\Repository\ThirdPartyRepository;
 use Chill\ThirdPartyBundle\Service\ThirdpartyMergeService;
 use Symfony\Bundle\FrameworkBundle\Controller\AbstractController;
 use Symfony\Component\HttpFoundation\Request;
 use Symfony\Component\Routing\Annotation\Route;
 use Sensio\Bundle\FrameworkExtraBundle\Configuration\ParamConverter;
+use Symfony\Contracts\Translation\TranslatorInterface;
 
 class ThirdpartyDuplicateController extends AbstractController
 {
-    public function __construct(private readonly ThirdPartyRepository $thirdPartyRepository, private readonly ThirdpartyMergeService $thirdPartyMergeService) {}
+    public function __construct(private readonly ThirdpartyMergeService $thirdPartyMergeService, private readonly TranslatorInterface $translator) {}
 
     /**
      * @ParamConverter("thirdparty", options={"id": "thirdparty_id"})
@@ -74,25 +74,45 @@ class ThirdpartyDuplicateController extends AbstractController
     #[Route(path: '/{_locale}/3party/{thirdparty1_id}/duplicate/{thirdparty2_id}/confirm', name: 'chill_thirdparty_duplicate_confirm')]
     public function confirmAction(ThirdParty $thirdparty1, ThirdParty $thirdparty2, Request $request)
     {
-        if ($thirdparty1 === $thirdparty2) {
-            throw new \InvalidArgumentException('Can not merge same thirdparty');
+        try {
+            $this->validateThirdpartyMerge($thirdparty1, $thirdparty2);
+            $form = $this->createForm(PersonConfimDuplicateType::class);
+
+            $form->handleRequest($request);
+
+            if ($form->isSubmitted() && $form->isValid()) {
+
+                $this->thirdPartyMergeService->merge($thirdparty1, $thirdparty2);
+
+                return $this->redirectToRoute('chill_crud_3party_3party_view', ['id' => $thirdparty1->getId()]);
+            }
+
+            return $this->render('@ChillThirdParty/ThirdPartyDuplicate/confirm.html.twig', [
+                'thirdparty' => $thirdparty1,
+                'thirdparty2' => $thirdparty2,
+                'form' => $form->createView(),
+            ]);
+        } catch (\InvalidArgumentException $e) {
+            $this->addFlash('error', $this->translator->trans($e->getMessage()));
+
+            return $this->redirectToRoute('chill_thirdparty_find_duplicate', [
+                'thirdparty_id' => $thirdparty1->getId(),
+            ]);
         }
+    }
 
-        $form = $this->createForm(PersonConfimDuplicateType::class);
+    private function validateThirdpartyMerge(Thirdparty $thirdparty1, Thirdparty $thirdparty2): void
+    {
+        $constraints = [
+            [$thirdparty1 === $thirdparty2, 'thirdparty_duplicate.You cannot merge a thirdparty with itself. Please choose a different thirdparty'],
+            [$thirdparty1->getKind() !== $thirdparty2->getKind(), 'thirdparty_duplicate.A thirdparty can only be merged with a thirdparty of the same kind'],
+            [$thirdparty1->getParent() !== $thirdparty2->getParent(), 'thirdparty_duplicate.Two child thirdparties must have the same parent'],
+        ];
 
-        $form->handleRequest($request);
-
-        if ($form->isSubmitted() && $form->isValid()) {
-
-            $this->thirdPartyMergeService->merge($thirdparty1, $thirdparty2);
-
-            return $this->redirectToRoute('chill_crud_3party_3party_view', ['id' => $thirdparty1->getId()]);
+        foreach ($constraints as [$condition, $message]) {
+            if ($condition) {
+                throw new \InvalidArgumentException($message);
+            }
         }
-
-        return $this->render('@ChillThirdParty/ThirdPartyDuplicate/confirm.html.twig', [
-            'thirdparty' => $thirdparty1,
-            'thirdparty2' => $thirdparty2,
-            'form' => $form->createView(),
-        ]);
     }
 }
diff --git a/src/Bundle/ChillThirdPartyBundle/Service/ThirdpartyMergeService.php b/src/Bundle/ChillThirdPartyBundle/Service/ThirdpartyMergeService.php
index 0c1d88e52..89412e5f6 100644
--- a/src/Bundle/ChillThirdPartyBundle/Service/ThirdpartyMergeService.php
+++ b/src/Bundle/ChillThirdPartyBundle/Service/ThirdpartyMergeService.php
@@ -90,7 +90,6 @@ class ThirdpartyMergeService
                     $joinColumn = $meta->getSingleAssociationJoinColumnName($assoc['fieldName']);
 
                     if (ThirdParty::class === $assoc['sourceEntity'] && 'parent_id' !== $joinColumn) {
-                        // TODO what with 'address_id' and 'civility_id'? This condition also contains columns like updatedBy_id which we want to ignore...
                         continue;
                     }
 
@@ -102,9 +101,7 @@ class ThirdpartyMergeService
                         'sql' => "UPDATE {$schemaPrefix}{$tableName} SET {$joinColumn} = :toKeep WHERE {$joinColumn} = :toDelete",
                         'params' => ['toKeep' => $toKeep->getId(), 'toDelete' => $toDelete->getId()],
                     ];
-                }
-
-                if ($assoc['type'] === 8 && isset($assoc['joinTable'])) {
+                } elseif (8 === $assoc['type'] && isset($assoc['joinTable'])) {
                     $joinTable = $assoc['joinTable']['name'];
                     $joinColumn = $assoc['joinTable']['joinColumns'][0]['name'];
                     $queries[] = [
diff --git a/src/Bundle/ChillThirdPartyBundle/translations/messages.fr.yml b/src/Bundle/ChillThirdPartyBundle/translations/messages.fr.yml
index b4340bde1..85f7b2405 100644
--- a/src/Bundle/ChillThirdPartyBundle/translations/messages.fr.yml
+++ b/src/Bundle/ChillThirdPartyBundle/translations/messages.fr.yml
@@ -141,3 +141,6 @@ thirdparty_duplicate:
     Thirdparty to delete explanation: Ce tiers sera supprimé. Seuls les contacts de ce tiers, énumérés ci-dessous, seront transférés.
     Thirdparty to keep explanation: Ce tiers sera conserver
     Data to keep: Données conservées
+    You cannot merge a thirdparty with itself. Please choose a different thirdparty: Vous ne pouvez pas fusionner un tiers avec lui-même. Veuillez choisir un autre tiers.
+    A thirdparty can only be merged with a thirdparty of the same kind: Un tiers ne peut être fusionné qu'avec un tiers de même type.
+    Two child thirdparties must have the same parent: Deux tiers de type « contact » doivent avoir le même tiers parent.