diff --git a/fixtures/WithArguments.php b/fixtures/WithArguments.php
index eb03aab72..fa787e5da 100644
--- a/fixtures/WithArguments.php
+++ b/fixtures/WithArguments.php
@@ -4,7 +4,7 @@
 
 class WithArguments
 {
-    public function methodWithArgs(\ArrayAccess $arg_1, array $arg_2 = [], \ArrayAccess $arg_3 = null)
+    public function methodWithArgs(\ArrayAccess $arg_1, array $arg_2 = [], ?\ArrayAccess $arg_3 = null)
     {
     }
     
diff --git a/fixtures/WithCallableArgument.php b/fixtures/WithCallableArgument.php
index 7d6d5f8f4..278aca20e 100644
--- a/fixtures/WithCallableArgument.php
+++ b/fixtures/WithCallableArgument.php
@@ -4,7 +4,7 @@
 
 class WithCallableArgument
 {
-    public function methodWithArgs(callable $arg_1, callable $arg_2 = null)
+    public function methodWithArgs(callable $arg_1, ?callable $arg_2 = null)
     {
     }
 }
diff --git a/src/Prophecy/Argument/Token/ExactValueToken.php b/src/Prophecy/Argument/Token/ExactValueToken.php
index e041cc3ca..a3d09ae78 100644
--- a/src/Prophecy/Argument/Token/ExactValueToken.php
+++ b/src/Prophecy/Argument/Token/ExactValueToken.php
@@ -36,7 +36,7 @@ class ExactValueToken implements TokenInterface
      *
      * @param mixed $value
      */
-    public function __construct($value, StringUtil $util = null, ComparatorFactory $comparatorFactory = null)
+    public function __construct($value, ?StringUtil $util = null, ?ComparatorFactory $comparatorFactory = null)
     {
         $this->value = $value;
         $this->util  = $util ?: new StringUtil();
diff --git a/src/Prophecy/Argument/Token/IdenticalValueToken.php b/src/Prophecy/Argument/Token/IdenticalValueToken.php
index 067d8775e..dbe253d97 100644
--- a/src/Prophecy/Argument/Token/IdenticalValueToken.php
+++ b/src/Prophecy/Argument/Token/IdenticalValueToken.php
@@ -32,7 +32,7 @@ class IdenticalValueToken implements TokenInterface
      *
      * @param mixed $value
      */
-    public function __construct($value, StringUtil $util = null)
+    public function __construct($value, ?StringUtil $util = null)
     {
         $this->value = $value;
         $this->util  = $util ?: new StringUtil();
diff --git a/src/Prophecy/Argument/Token/ObjectStateToken.php b/src/Prophecy/Argument/Token/ObjectStateToken.php
index 49dea6838..bb0586395 100644
--- a/src/Prophecy/Argument/Token/ObjectStateToken.php
+++ b/src/Prophecy/Argument/Token/ObjectStateToken.php
@@ -37,8 +37,8 @@ class ObjectStateToken implements TokenInterface
     public function __construct(
         $methodName,
         $value,
-        StringUtil $util = null,
-        ComparatorFactory $comparatorFactory = null
+        ?StringUtil $util = null,
+        ?ComparatorFactory $comparatorFactory = null
     ) {
         $this->name  = $methodName;
         $this->value = $value;
diff --git a/src/Prophecy/Call/Call.php b/src/Prophecy/Call/Call.php
index 625f62ae6..486b03a20 100644
--- a/src/Prophecy/Call/Call.php
+++ b/src/Prophecy/Call/Call.php
@@ -49,7 +49,7 @@ class Call
      * @param null|int    $line
      */
     public function __construct($methodName, array $arguments, $returnValue,
-                                Exception $exception = null, $file, $line)
+                                ?Exception $exception, $file, $line)
     {
         $this->methodName  = $methodName;
         $this->arguments   = $arguments;
diff --git a/src/Prophecy/Call/CallCenter.php b/src/Prophecy/Call/CallCenter.php
index e2d0b98f2..d485fd2d4 100644
--- a/src/Prophecy/Call/CallCenter.php
+++ b/src/Prophecy/Call/CallCenter.php
@@ -43,7 +43,7 @@ class CallCenter
      *
      * @param StringUtil $util
      */
-    public function __construct(StringUtil $util = null)
+    public function __construct(?StringUtil $util = null)
     {
         $this->util = $util ?: new StringUtil;
         $this->unexpectedCalls = new SplObjectStorage();
diff --git a/src/Prophecy/Doubler/CachedDoubler.php b/src/Prophecy/Doubler/CachedDoubler.php
index f6f2ce66a..df892d3b7 100644
--- a/src/Prophecy/Doubler/CachedDoubler.php
+++ b/src/Prophecy/Doubler/CachedDoubler.php
@@ -26,7 +26,7 @@ class CachedDoubler extends Doubler
      */
     private static $classes = array();
 
-    protected function createDoubleClass(ReflectionClass $class = null, array $interfaces)
+    protected function createDoubleClass(?ReflectionClass $class, array $interfaces)
     {
         $classId = $this->generateClassId($class, $interfaces);
         if (isset(self::$classes[$classId])) {
@@ -42,7 +42,7 @@ protected function createDoubleClass(ReflectionClass $class = null, array $inter
      *
      * @return string
      */
-    private function generateClassId(ReflectionClass $class = null, array $interfaces)
+    private function generateClassId(?ReflectionClass $class, array $interfaces)
     {
         $parts = array();
         if (null !== $class) {
diff --git a/src/Prophecy/Doubler/ClassPatch/MagicCallPatch.php b/src/Prophecy/Doubler/ClassPatch/MagicCallPatch.php
index f4c3d8b58..50299e7d5 100644
--- a/src/Prophecy/Doubler/ClassPatch/MagicCallPatch.php
+++ b/src/Prophecy/Doubler/ClassPatch/MagicCallPatch.php
@@ -30,7 +30,7 @@ class MagicCallPatch implements ClassPatchInterface
 
     private $tagRetriever;
 
-    public function __construct(MethodTagRetrieverInterface $tagRetriever = null)
+    public function __construct(?MethodTagRetrieverInterface $tagRetriever = null)
     {
         $this->tagRetriever = null === $tagRetriever ? new ClassAndInterfaceTagRetriever() : $tagRetriever;
     }
diff --git a/src/Prophecy/Doubler/Doubler.php b/src/Prophecy/Doubler/Doubler.php
index 88e153093..9cc4337ee 100644
--- a/src/Prophecy/Doubler/Doubler.php
+++ b/src/Prophecy/Doubler/Doubler.php
@@ -40,8 +40,8 @@ class Doubler
      */
     private $instantiator;
 
-    public function __construct(ClassMirror $mirror = null, ClassCreator $creator = null,
-                                NameGenerator $namer = null)
+    public function __construct(?ClassMirror $mirror = null, ?ClassCreator $creator = null,
+                                ?NameGenerator $namer = null)
     {
         $this->mirror  = $mirror  ?: new ClassMirror;
         $this->creator = $creator ?: new ClassCreator;
@@ -87,7 +87,7 @@ public function registerClassPatch(ClassPatchInterface $patch)
      *
      * @throws \Prophecy\Exception\InvalidArgumentException
      */
-    public function double(ReflectionClass $class = null, array $interfaces, array $args = null)
+    public function double(?ReflectionClass $class, array $interfaces, ?array $args = null)
     {
         foreach ($interfaces as $interface) {
             if (!$interface instanceof ReflectionClass) {
@@ -127,7 +127,7 @@ public function double(ReflectionClass $class = null, array $interfaces, array $
      *
      * @return class-string<T&DoubleInterface>
      */
-    protected function createDoubleClass(ReflectionClass $class = null, array $interfaces)
+    protected function createDoubleClass(?ReflectionClass $class, array $interfaces)
     {
         $name = $this->namer->name($class, $interfaces);
         $node = $this->mirror->reflect($class, $interfaces);
diff --git a/src/Prophecy/Doubler/Generator/ClassCreator.php b/src/Prophecy/Doubler/Generator/ClassCreator.php
index 79f3b95de..1ebc32c88 100644
--- a/src/Prophecy/Doubler/Generator/ClassCreator.php
+++ b/src/Prophecy/Doubler/Generator/ClassCreator.php
@@ -23,7 +23,7 @@ class ClassCreator
 {
     private $generator;
 
-    public function __construct(ClassCodeGenerator $generator = null)
+    public function __construct(?ClassCodeGenerator $generator = null)
     {
         $this->generator = $generator ?: new ClassCodeGenerator;
     }
diff --git a/src/Prophecy/Doubler/LazyDouble.php b/src/Prophecy/Doubler/LazyDouble.php
index 96ca25bb7..e794293cb 100644
--- a/src/Prophecy/Doubler/LazyDouble.php
+++ b/src/Prophecy/Doubler/LazyDouble.php
@@ -125,7 +125,7 @@ public function addInterface($interface)
      *
      * @return void
      */
-    public function setArguments(array $arguments = null)
+    public function setArguments(?array $arguments = null)
     {
         $this->arguments = $arguments;
     }
diff --git a/src/Prophecy/Doubler/NameGenerator.php b/src/Prophecy/Doubler/NameGenerator.php
index b62006493..b99366474 100644
--- a/src/Prophecy/Doubler/NameGenerator.php
+++ b/src/Prophecy/Doubler/NameGenerator.php
@@ -34,7 +34,7 @@ class NameGenerator
      *
      * @return string
      */
-    public function name(ReflectionClass $class = null, array $interfaces)
+    public function name(?ReflectionClass $class, array $interfaces)
     {
         $parts = array();
 
diff --git a/src/Prophecy/PhpDocumentor/ClassAndInterfaceTagRetriever.php b/src/Prophecy/PhpDocumentor/ClassAndInterfaceTagRetriever.php
index c4eccfcdc..7b6153524 100644
--- a/src/Prophecy/PhpDocumentor/ClassAndInterfaceTagRetriever.php
+++ b/src/Prophecy/PhpDocumentor/ClassAndInterfaceTagRetriever.php
@@ -25,7 +25,7 @@ final class ClassAndInterfaceTagRetriever implements MethodTagRetrieverInterface
      */
     private $classRetriever;
 
-    public function __construct(MethodTagRetrieverInterface $classRetriever = null)
+    public function __construct(?MethodTagRetrieverInterface $classRetriever = null)
     {
         if (null !== $classRetriever) {
             $this->classRetriever = $classRetriever;
diff --git a/src/Prophecy/Prediction/CallPrediction.php b/src/Prophecy/Prediction/CallPrediction.php
index a6b95a3bd..cc853771f 100644
--- a/src/Prophecy/Prediction/CallPrediction.php
+++ b/src/Prophecy/Prediction/CallPrediction.php
@@ -28,7 +28,7 @@ class CallPrediction implements PredictionInterface
 {
     private $util;
 
-    public function __construct(StringUtil $util = null)
+    public function __construct(?StringUtil $util = null)
     {
         $this->util = $util ?: new StringUtil;
     }
diff --git a/src/Prophecy/Prediction/CallTimesPrediction.php b/src/Prophecy/Prediction/CallTimesPrediction.php
index 19554f30a..9aa30ca8f 100644
--- a/src/Prophecy/Prediction/CallTimesPrediction.php
+++ b/src/Prophecy/Prediction/CallTimesPrediction.php
@@ -32,7 +32,7 @@ class CallTimesPrediction implements PredictionInterface
     /**
      * @param int        $times
      */
-    public function __construct($times, StringUtil $util = null)
+    public function __construct($times, ?StringUtil $util = null)
     {
         $this->times = intval($times);
         $this->util  = $util ?: new StringUtil;
diff --git a/src/Prophecy/Prediction/NoCallsPrediction.php b/src/Prophecy/Prediction/NoCallsPrediction.php
index b1b4f9fdd..dee384c19 100644
--- a/src/Prophecy/Prediction/NoCallsPrediction.php
+++ b/src/Prophecy/Prediction/NoCallsPrediction.php
@@ -26,7 +26,7 @@ class NoCallsPrediction implements PredictionInterface
 {
     private $util;
 
-    public function __construct(StringUtil $util = null)
+    public function __construct(?StringUtil $util = null)
     {
         $this->util = $util ?: new StringUtil;
     }
diff --git a/src/Prophecy/Prophecy/ObjectProphecy.php b/src/Prophecy/Prophecy/ObjectProphecy.php
index d10332f71..582a405ff 100644
--- a/src/Prophecy/Prophecy/ObjectProphecy.php
+++ b/src/Prophecy/Prophecy/ObjectProphecy.php
@@ -49,9 +49,9 @@ class ObjectProphecy implements ProphecyInterface
      */
     public function __construct(
         LazyDouble $lazyDouble,
-        CallCenter $callCenter = null,
-        RevealerInterface $revealer = null,
-        ComparatorFactory $comparatorFactory = null
+        ?CallCenter $callCenter = null,
+        ?RevealerInterface $revealer = null,
+        ?ComparatorFactory $comparatorFactory = null
     ) {
         $this->lazyDouble = $lazyDouble;
         $this->callCenter = $callCenter ?: new CallCenter;
@@ -103,7 +103,7 @@ public function willImplement($interface)
      *
      * @return $this
      */
-    public function willBeConstructedWith(array $arguments = null)
+    public function willBeConstructedWith(?array $arguments = null)
     {
         $this->lazyDouble->setArguments($arguments);
 
diff --git a/src/Prophecy/Prophet.php b/src/Prophecy/Prophet.php
index 16c781347..2b2c77d13 100644
--- a/src/Prophecy/Prophet.php
+++ b/src/Prophecy/Prophet.php
@@ -44,9 +44,9 @@ class Prophet
     private $prophecies = array();
 
     public function __construct(
-        Doubler $doubler = null,
-        RevealerInterface $revealer = null,
-        StringUtil $util = null
+        ?Doubler $doubler = null,
+        ?RevealerInterface $revealer = null,
+        ?StringUtil $util = null
     ) {
         if (null === $doubler) {
             $doubler = new CachedDoubler();