diff --git a/src/Phpunit/MockedFunction.php b/src/Phpunit/MockedFunction.php
index a4d2527..8f31f89 100644
--- a/src/Phpunit/MockedFunction.php
+++ b/src/Phpunit/MockedFunction.php
@@ -30,7 +30,7 @@ class MockedFunction extends AbstractMocked
     public function __construct(
         TestCase $testCase,
         string $function,
-        InvocationOrder $invocationRule = null
+        ?InvocationOrder $invocationRule = null
     ) {
         $mockObject = null;
         $method     = null;
diff --git a/src/Phpunit/MockedMethod.php b/src/Phpunit/MockedMethod.php
index e414514..119ef30 100644
--- a/src/Phpunit/MockedMethod.php
+++ b/src/Phpunit/MockedMethod.php
@@ -45,7 +45,7 @@ public function __construct(
         TestCase $testCase,
         string $class,
         string $method,
-        InvocationOrder $invocationRule = null
+        ?InvocationOrder $invocationRule = null
     ) {
         $this->mockObject = self::createEmptyMock($testCase, $method);