diff --git a/src/LanguageServer.php b/src/LanguageServer.php
index a2c1f52..939bc99 100644
--- a/src/LanguageServer.php
+++ b/src/LanguageServer.php
@@ -107,12 +107,13 @@ class LanguageServer extends AdvancedJsonRpc\Dispatcher
     /**
      * The initialize request is sent as the first request from the client to the server.
      *
-     * @param int $processId The process Id of the parent process that started the server.
      * @param ClientCapabilities $capabilities The capabilities provided by the client (editor)
      * @param string|null $rootPath The rootPath of the workspace. Is null if no folder is open.
+	 * @param int|null $processId The process Id of the parent process that started the server. Is null if the process has not
+	 *          been started by another process. If the parent process is not alive then the server should exit (see exit notification) its process.
      * @return InitializeResult
      */
-    public function initialize(int $processId, ClientCapabilities $capabilities, string $rootPath = null): InitializeResult
+    public function initialize(ClientCapabilities $capabilities, string $rootPath = null, int $processId = null): InitializeResult
     {
         $this->rootPath = $rootPath;
         $this->clientCapabilities = $capabilities;