diff --git a/src/PhpOption/Option.php b/src/PhpOption/Option.php
index bdc215f..c69e43a 100644
--- a/src/PhpOption/Option.php
+++ b/src/PhpOption/Option.php
@@ -93,7 +93,7 @@ public static function fromArraysValue($array, $key)
      */
     public static function fromReturn($callback, array $arguments = [], $noneValue = null)
     {
-        return new LazyOption(function () use ($callback, $arguments, $noneValue) {
+        return new LazyOption(static function () use ($callback, $arguments, $noneValue) {
             /** @var mixed */
             $return = call_user_func_array($callback, $arguments);
 
@@ -126,7 +126,7 @@ public static function ensure($value, $noneValue = null)
         if ($value instanceof self) {
             return $value;
         } elseif (is_callable($value)) {
-            return new LazyOption(function () use ($value, $noneValue) {
+            return new LazyOption(static function () use ($value, $noneValue) {
                 /** @var mixed */
                 $return = $value();
 
@@ -159,14 +159,14 @@ public static function ensure($value, $noneValue = null)
      */
     public static function lift($callback, $noneValue = null)
     {
-        return function () use ($callback, $noneValue) {
+        return static function () use ($callback, $noneValue) {
             /** @var array<int, mixed> */
             $args = func_get_args();
 
             $reduced_args = array_reduce(
                 $args,
                 /** @param bool $status */
-                function ($status, self $o) {
+                static function ($status, self $o) {
                     return $o->isEmpty() ? true : $status;
                 },
                 false
@@ -178,7 +178,7 @@ function ($status, self $o) {
 
             $args = array_map(
                 /** @return T */
-                function (self $o) {
+                static function (self $o) {
                     // it is safe to do so because the fold above checked
                     // that all arguments are of type Some
                     /** @var T */