diff --git a/src/Prophecy/Doubler/Generator/ClassCodeGenerator.php b/src/Prophecy/Doubler/Generator/ClassCodeGenerator.php
index ddc6985c..a34ad0f4 100644
--- a/src/Prophecy/Doubler/Generator/ClassCodeGenerator.php
+++ b/src/Prophecy/Doubler/Generator/ClassCodeGenerator.php
@@ -11,6 +11,7 @@
 
 namespace Prophecy\Doubler\Generator;
 
+use Prophecy\Doubler\Generator\Node\ArgumentTypeNode;
 use Prophecy\Doubler\Generator\Node\ReturnTypeNode;
 use Prophecy\Doubler\Generator\Node\TypeNodeAbstract;
 
@@ -78,14 +79,14 @@ private function generateMethod(Node\MethodNode $method): string
         return $php.'}';
     }
 
-    private function generateTypes(TypeNodeAbstract $typeNode): string
+    private function generateTypes(TypeNodeAbstract $typeNode, bool $nullable = FALSE): string
     {
         if (!$typeNode->getTypes()) {
             return '';
         }
 
         // When we require PHP 8 we can stop generating ?foo nullables and remove this first block
-        if ($typeNode->canUseNullShorthand()) {
+        if ($typeNode->canUseNullShorthand() || $nullable) {
             return sprintf( '?%s', $typeNode->getNonNullTypes()[0]);
         } else {
             return join('|', $typeNode->getTypes());
@@ -101,7 +102,18 @@ private function generateArguments(array $arguments): array
     {
         return array_map(function (Node\ArgumentNode $argument){
 
-            $php = $this->generateTypes($argument->getTypeNode());
+            $types = $argument->getTypeNode()->getTypes();
+            if ($nullable = $argument->isOptional() && $argument->getDefault() === NULL) {
+              $count = \count($types);
+              if ($count === 1 && $types[0] === 'mixed' ) {
+                $nullable = FALSE;
+              }
+              elseif ($count > 1 && !isset($types['null'])) {
+                $argument->setTypeNode(new ArgumentTypeNode('null', ...$argument->getTypeNode()->getNonNullTypes()));
+                $nullable = FALSE;
+              }
+            }
+            $php = $this->generateTypes($argument->getTypeNode(), $nullable);
 
             $php .= ' '.($argument->isPassedByReference() ? '&' : '');