diff --git a/Component/TicketFeatures.php b/Component/TicketFeatures.php
index 85597582..3ae72f4d 100644
--- a/Component/TicketFeatures.php
+++ b/Component/TicketFeatures.php
@@ -18,10 +18,14 @@
  */
 class TicketFeatures
 {
-    private $features;
+    /**
+     * @var array<string, bool>
+     */
+    private $features = [];
 
     /**
-     * @param string $messageClass TicketMessage class
+     * @param array<string, bool> $features
+     * @param string              $messageClass TicketMessage class
      */
     public function __construct(array $features, $messageClass)
     {
@@ -34,18 +38,31 @@ public function __construct(array $features, $messageClass)
     }
 
     /**
+     * NEXT_MAJOR: Remove the BC checks and return only boolean values.
+     *
      * Check if feature exists or whether enabled.
      *
-     * @param $feature
+     * @param string $feature
      *
      * @return bool|null
      */
     public function hasFeature($feature)
     {
+        $args = \func_get_args();
+        if (isset($args[1]) && 'return_strict_bool' === $args[1]) {
+            return isset($this->features[$feature]) && $this->features[$feature];
+        }
+
         if (!isset($this->features[$feature])) {
+            @trigger_error(sprintf(
+                'Returning other type than boolean from "%s()" is deprecated since hackzilla/ticket-bundle 3.x'
+                .' and will be not allowed in version 4.0.',
+                __METHOD__
+            ), E_USER_DEPRECATED);
+
             return null;
         }
 
-        return $this->features[$feature];
+        return (bool) $this->features[$feature];
     }
 }
diff --git a/Form/Type/TicketMessageType.php b/Form/Type/TicketMessageType.php
index 3b4d6466..7a2901db 100644
--- a/Form/Type/TicketMessageType.php
+++ b/Form/Type/TicketMessageType.php
@@ -59,7 +59,8 @@ public function buildForm(FormBuilderInterface $builder, array $options)
                 ]
             );
 
-        if ($this->features->hasFeature('attachment')) {
+        // NEXT_MAJOR: Remove the argument 2 for `TicketFeatures::hasFeature()`
+        if ($this->features->hasFeature('attachment', 'return_strict_bool')) {
             $builder
                 ->add(
                     'attachmentFile',
diff --git a/Tests/Component/TicketFeaturesTest.php b/Tests/Component/TicketFeaturesTest.php
index 1aa3e5df..40df5c37 100644
--- a/Tests/Component/TicketFeaturesTest.php
+++ b/Tests/Component/TicketFeaturesTest.php
@@ -21,20 +21,17 @@ final class TicketFeaturesTest extends WebTestCase
     /**
      * @dataProvider constructProvider
      *
-     * @param array  $features
      * @param string $class
      */
-    public function testConstruct($features, $class)
+    public function testConstruct(array $features, $class)
     {
-        $obj = new TicketFeatures($features, $class);
-
-        $this->assertInstanceOf(TicketFeatures::class, $obj);
+        $this->assertInstanceOf(TicketFeatures::class, new TicketFeatures($features, $class));
     }
 
     public function constructProvider()
     {
         return [
-            [[], '\stdClass'],
+            [[], \stdClass::class],
         ];
     }
 
@@ -49,13 +46,14 @@ public function testFeatureAttachment(array $features, $class, $compare)
         $obj = new TicketFeatures($features, $class);
 
         $this->assertInstanceOf(TicketFeatures::class, $obj);
-        $this->assertSame($obj->hasFeature('attachment'), $compare);
+        // NEXT_MAJOR: Remove the argument 2 for `TicketFeatures::hasFeature()`
+        $this->assertSame($obj->hasFeature('attachment', 'return_strict_bool'), $compare);
     }
 
     public function featureAttachmentProvider()
     {
         return [
-            [[], TicketMessage::class, null],
+            [[], TicketMessage::class, false],
             [['attachment' => true], TicketMessage::class, false],
             [['attachment' => true], TicketMessageWithAttachment::class, true],
         ];
diff --git a/UPGRADE-3.x.md b/UPGRADE-3.x.md
index d1007f4e..46e9ad1b 100644
--- a/UPGRADE-3.x.md
+++ b/UPGRADE-3.x.md
@@ -1,3 +1,11 @@
+UPGRADE FROM 3.5 to 3.6
+=======================
+
+## `Hackzilla\Bundle\TicketBundle\Component\TicketFeatures`
+
+Returning other type than boolean from `TicketFeatures::hasFeature()` is deprecated
+and will be not allowed in version 4.0.
+
 UPGRADE FROM 3.4 to 3.5
 =======================