diff --git a/src/DocBlock/Tags/Factory/MethodFactory.php b/src/DocBlock/Tags/Factory/MethodFactory.php
index 51dc042..5d90759 100644
--- a/src/DocBlock/Tags/Factory/MethodFactory.php
+++ b/src/DocBlock/Tags/Factory/MethodFactory.php
@@ -57,7 +57,7 @@ final class MethodFactory implements PHPStanFactory
                         ),
                         $param->isReference,
                         $param->isVariadic,
-                        $param->defaultValue
+                        $param->defaultValue === null ? MethodParameter::NO_DEFAULT_VALUE : (string) $param->defaultValue
                     );
                 },
                 $tagValue->parameters
diff --git a/src/DocBlock/Tags/MethodParameter.php b/src/DocBlock/Tags/MethodParameter.php
index c50c87e..2cb8177 100644
--- a/src/DocBlock/Tags/MethodParameter.php
+++ b/src/DocBlock/Tags/MethodParameter.php
@@ -30,7 +30,7 @@ final class MethodParameter
      */
     private $defaultValue;
 
-    private const NO_DEFAULT_VALUE = '__NO_VALUE__';
+    public const NO_DEFAULT_VALUE = '__NO_VALUE__';
 
     /**
      * @param mixed $defaultValue