diff --git a/Admin/Routes/Web/Backend.php b/Admin/Routes/Web/Backend.php
index 4ce3d28..1b8d124 100644
--- a/Admin/Routes/Web/Backend.php
+++ b/Admin/Routes/Web/Backend.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 use Modules\Calendar\Controller\BackendController;
 use Modules\Calendar\Models\PermissionState;
diff --git a/Theme/Backend/Lang/Navigation.en.lang.php b/Theme/Backend/Lang/Navigation.en.lang.php
index 397ac41..0ba3883 100644
--- a/Theme/Backend/Lang/Navigation.en.lang.php
+++ b/Theme/Backend/Lang/Navigation.en.lang.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 /**
  * Orange Management
  *
diff --git a/Theme/Backend/Lang/api.en.lang.php b/Theme/Backend/Lang/api.en.lang.php
index 959dc12..763b2bb 100644
--- a/Theme/Backend/Lang/api.en.lang.php
+++ b/Theme/Backend/Lang/api.en.lang.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 /**
  * Orange Management
  *
diff --git a/Theme/Backend/Lang/en.lang.php b/Theme/Backend/Lang/en.lang.php
index e532497..f5e2faa 100644
--- a/Theme/Backend/Lang/en.lang.php
+++ b/Theme/Backend/Lang/en.lang.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 /**
  * Orange Management
  *
diff --git a/Theme/Backend/calendar-dashboard.tpl.php b/Theme/Backend/calendar-dashboard.tpl.php
index f251ab8..71c58c3 100644
--- a/Theme/Backend/calendar-dashboard.tpl.php
+++ b/Theme/Backend/calendar-dashboard.tpl.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 $calendar = $this->getData('calendar');
 ?>
 <div class="row">
diff --git a/Theme/Backend/dashboard-calendar.tpl.php b/Theme/Backend/dashboard-calendar.tpl.php
index c60d216..1ee02ef 100644
--- a/Theme/Backend/dashboard-calendar.tpl.php
+++ b/Theme/Backend/dashboard-calendar.tpl.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 /**
  * Orange Management
  *