diff --git a/CHANGELOG.md b/CHANGELOG.md
index 99b1fc6..2d561a9 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -15,6 +15,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
  - Custom route to load map data.
  - Add distance filter support for the marker layer (Bounds Mode "fit" has to be enabled).
  - Add support for relative css units for map size definition (#59).
+ - Add hint that zoom level is probably required (#56).
 
 ### Deprecated
 
@@ -23,6 +24,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
  
 ### Changed
 
+ - Require PHP 7.1.
  - Rewritten about page using own route (#48).
 
 ### Fixed
diff --git a/src/Bundle/Resources/config/listeners.yml b/src/Bundle/Resources/config/listeners.yml
index afd2b09..692bc00 100644
--- a/src/Bundle/Resources/config/listeners.yml
+++ b/src/Bundle/Resources/config/listeners.yml
@@ -30,6 +30,8 @@ services:
       - '@netzmacht.contao_toolkit.dca.manager'
       - '@database_connection'
       - '@netzmacht.contao_toolkit.repository_manager'
+      - '@translator'
+      - '@session'
 
   netzmacht.contao_leaflet.listeners.dca.control:
     class: Netzmacht\Contao\Leaflet\Listener\Dca\ControlDcaListener
diff --git a/src/Bundle/Resources/contao/dca/tl_leaflet_map.php b/src/Bundle/Resources/contao/dca/tl_leaflet_map.php
index 6b701f2..c293b32 100644
--- a/src/Bundle/Resources/contao/dca/tl_leaflet_map.php
+++ b/src/Bundle/Resources/contao/dca/tl_leaflet_map.php
@@ -23,6 +23,7 @@ $GLOBALS['TL_DCA']['tl_leaflet_map'] = [
         ],
         'onload_callback'   => [
             ['netzmacht.contao_leaflet.listeners.dca.leaflet', 'loadLanguageFile'],
+            ['netzmacht.contao_leaflet.listeners.dca.map', 'addIncompleteConfigurationWarning'],
         ],
         'onsubmit_callback' => [
             ['netzmacht.contao_leaflet.listeners.dca.leaflet', 'clearCache'],
diff --git a/src/Bundle/Resources/contao/languages/en/default.php b/src/Bundle/Resources/contao/languages/en/default.php
new file mode 100644
index 0000000..fc4b709
--- /dev/null
+++ b/src/Bundle/Resources/contao/languages/en/default.php
@@ -0,0 +1,15 @@
+<?php
+
+/**
+ * Leaflet maps for Contao CMS.
+ *
+ * @package    contao-leaflet-maps
+ * @author     David Molineus <david.molineus@netzmacht.de>
+ * @copyright  2014-2018 netzmacht David Molineus. All rights reserved.
+ * @license    LGPL-3.0 https://github.com/netzmacht/contao-leaflet-maps/blob/master/LICENSE
+ * @filesource
+ */
+
+declare(strict_types=1);
+
+$GLOBALS['TL_LANG']['ERR']['leafletMissingZoomLevel'] = 'No zoom level defined. Only leave it empty on purpose (Zoom level might by initialized by bounds adjustments). Otherwise no map will be shown.';
diff --git a/src/Listener/Dca/MapDcaListener.php b/src/Listener/Dca/MapDcaListener.php
index 2a4077e..fa74ef4 100644
--- a/src/Listener/Dca/MapDcaListener.php
+++ b/src/Listener/Dca/MapDcaListener.php
@@ -15,14 +15,20 @@ declare(strict_types=1);
 namespace Netzmacht\Contao\Leaflet\Listener\Dca;
 
 use Contao\DataContainer;
+use Contao\Input;
 use Contao\StringUtil;
 use Doctrine\DBAL\Connection;
 use Netzmacht\Contao\Leaflet\Model\LayerModel;
+use Netzmacht\Contao\Leaflet\Model\MapModel;
 use Netzmacht\Contao\Toolkit\Data\Model\RepositoryManager;
 use Netzmacht\Contao\Toolkit\Dca\Listener\AbstractListener;
 use Netzmacht\Contao\Toolkit\Dca\Manager;
 use Netzmacht\Contao\Toolkit\Dca\Options\OptionsBuilder;
 use PDO;
+use function strlen;
+use Symfony\Component\HttpFoundation\Session\Session;
+use Symfony\Component\Translation\TranslatorInterface as Translator;
+use function var_dump;
 
 /**
  * Class Map is the helper class for the tl_leaflet_map dca.
@@ -52,19 +58,70 @@ class MapDcaListener extends AbstractListener
      */
     private $repositoryManager;
 
+    /**
+     * Translator.
+     *
+     * @var Translator
+     */
+    private $translator;
+
+    /**
+     * Session.
+     *
+     * @var Session
+     */
+    private $session;
+
     /**
      * Construct.
      *
      * @param Manager           $manager           Data container manager.
      * @param Connection        $connection        Database connection.
      * @param RepositoryManager $repositoryManager Repository manager.
+     * @param Translator        $translator        Translator.
+     * @param Session           $session           Session.
      */
-    public function __construct(Manager $manager, Connection $connection, RepositoryManager $repositoryManager)
-    {
+    public function __construct(
+        Manager $manager,
+        Connection $connection,
+        RepositoryManager $repositoryManager,
+        Translator $translator,
+        Session $session
+    ) {
         parent::__construct($manager);
 
         $this->connection        = $connection;
         $this->repositoryManager = $repositoryManager;
+        $this->translator        = $translator;
+        $this->session           = $session;
+    }
+
+    /**
+     * Add warnings for incomplete configurations.
+     *
+     * @param DataContainer $dataContainer The data container driver.
+     *
+     * @return void
+     */
+    public function addIncompleteConfigurationWarning($dataContainer): void
+    {
+        if (Input::get('act') !== 'edit') {
+            return;
+        }
+
+        $repository = $this->repositoryManager->getRepository(MapModel::class);
+        $map        = $repository->find((int) $dataContainer->id);
+
+        if (!$map) {
+            return;
+        }
+
+        if ($map->zoom === null || $map->zoom === '') {
+            $this->session->getFlashBag()->add(
+                'contao.BE.info',
+                $this->translator->trans('ERR.leafletMissingZoomLevel', [], 'contao_default')
+            );
+        }
     }
 
     /**