diff --git a/src/Feature.php b/src/Feature.php
index ba68a1e..c0a3b08 100644
--- a/src/Feature.php
+++ b/src/Feature.php
@@ -216,7 +216,7 @@ public function clear()
      * @param array $requestParameters
      * @return bool
      */
-    public function isActive(Rollout $rollout, RolloutUserInterface $user = null, array $requestParameters = array())
+    public function isActive(Rollout $rollout, ?RolloutUserInterface $user = null, array $requestParameters = array())
     {
         if (null == $user) {
             return $this->isParamInRequestParams($requestParameters)
@@ -281,7 +281,7 @@ private function isUserInActiveUsers(RolloutUserInterface $user)
      * @param RolloutUserInterface|null $user
      * @return bool
      */
-    private function isInActiveGroup(Rollout $rollout, RolloutUserInterface $user = null)
+    private function isInActiveGroup(Rollout $rollout, ?RolloutUserInterface $user = null)
     {
         foreach ($this->groups as $group) {
             if ($rollout->isActiveInGroup($group, $user)) {
diff --git a/src/Rollout.php b/src/Rollout.php
index c5d8db5..cc33fa4 100644
--- a/src/Rollout.php
+++ b/src/Rollout.php
@@ -124,7 +124,7 @@ public function defineGroup($group, \Closure $closure)
      * @param array $requestParameters
      * @return bool
      */
-    public function isActive($feature, RolloutUserInterface $user = null, array $requestParameters = array())
+    public function isActive($feature, ?RolloutUserInterface $user = null, array $requestParameters = array())
     {
         $feature = $this->get($feature);
 
@@ -186,7 +186,7 @@ public function deactivateRequestParam($feature)
      * @param RolloutUserInterface|null $user
      * @return bool
      */
-    public function isActiveInGroup($group, RolloutUserInterface $user = null)
+    public function isActiveInGroup($group, ?RolloutUserInterface $user = null)
     {
         if (!isset($this->groups[$group])) {
             return false;