diff --git a/src/Pug/AbstractFilter.php b/src/Pug/AbstractFilter.php
index 3497ddfc0ca087a6f3e64c8002653d15efdaff6a..6273abfc501a23020be547235a86c803f92fd7fe 100644
--- a/src/Pug/AbstractFilter.php
+++ b/src/Pug/AbstractFilter.php
@@ -9,7 +9,7 @@ use Pug\Filter\AbstractFilterBase;
  */
 abstract class AbstractFilter extends AbstractFilterBase implements FilterInterface
 {
-    public function __invoke($code, array $options = null)
+    public function __invoke($code, ?array $options = null)
     {
         return $this->pugInvoke($code, $options);
     }
diff --git a/src/Pug/Filter/AbstractFilterBase.php b/src/Pug/Filter/AbstractFilterBase.php
index 277c50d1ea76fea4279145d8308d7a6c3b8ff5d1..867232babc4b0c43d29b6dfef5a868b9f1fff5c4 100644
--- a/src/Pug/Filter/AbstractFilterBase.php
+++ b/src/Pug/Filter/AbstractFilterBase.php
@@ -9,7 +9,7 @@ abstract class AbstractFilterBase
 {
     use WrapTagTrait;
 
-    public function pugInvoke($code, array $options = null)
+    public function pugInvoke($code, ?array $options = null)
     {
         if (method_exists($this, 'parse')) {
             $code = $this->parse($code, $options);
diff --git a/src/Pug/Filter/Php.php b/src/Pug/Filter/Php.php
index da0e81b5612fad4222da7e60441f417082c94e1b..8426b6d4b414423cf46292b016d507c6ce1a6eae 100644
--- a/src/Pug/Filter/Php.php
+++ b/src/Pug/Filter/Php.php
@@ -9,7 +9,7 @@ use Pug\FilterInterface as FilterBase;
  */
 class Php implements FilterBase
 {
-    public function __invoke($code, array $options = null)
+    public function __invoke($code, ?array $options = null)
     {
         return "<?php\n$code\n?>";
     }
diff --git a/src/Pug/FilterInterface.php b/src/Pug/FilterInterface.php
index 62227798af30bacafbd86d3919aa2bf32a8521f0..900aa4df681c3e9fe83122a2de3f54b23c0041b5 100644
--- a/src/Pug/FilterInterface.php
+++ b/src/Pug/FilterInterface.php
@@ -13,5 +13,5 @@ interface FilterInterface
      *
      * @return string
      */
-    public function __invoke($code, array $options = null);
+    public function __invoke($code, ?array $options = null);
 }