diff --git a/app/Model/Facade/FakturaFacade.php b/app/Model/Facade/FakturaFacade.php
index 6ca61a7..41df1e4 100644
--- a/app/Model/Facade/FakturaFacade.php
+++ b/app/Model/Facade/FakturaFacade.php
@@ -108,6 +108,10 @@ class FakturaFacade
             $zakaznikId = !empty($data['ZAKAZNIK_ID']) ? (int) $data['ZAKAZNIK_ID'] : null;
             $zakaznik = $zakaznikId ? $this->kufrikExplorer->table('ZAKAZNIK')->where('ID', $zakaznikId)->fetch() : null;
 
+            if (!$zakaznikId || !$zakaznik) {
+                throw new \InvalidArgumentException('Faktura musí mít odběratele.');
+            }
+
             $oPrajm = $zakaznik ? trim(($zakaznik->PRIJMENI ?? '') . ' ' . ($zakaznik->JMENO ?? '')) : null;
 
             $dBanka = null;
diff --git a/app/UI/FakturaEdit/FakturaEditPresenter.php b/app/UI/FakturaEdit/FakturaEditPresenter.php
index e2088ee..393ce91 100644
--- a/app/UI/FakturaEdit/FakturaEditPresenter.php
+++ b/app/UI/FakturaEdit/FakturaEditPresenter.php
@@ -107,7 +107,8 @@ class FakturaEditPresenter extends BasePresenter
         }
 
         $form->addSelect('ZAKAZNIK_ID', 'Odběratel:', $zakazniciPairs)
-            ->setPrompt('-- Vyberte zákazníka --');
+            ->setPrompt('-- Vyberte zákazníka --')
+            ->setRequired('Vyberte odběratele.');
 
         $form->addText('CISLO', 'Číslo faktury:')
             ->setDefaultValue(date('Y') . '001');