diff --git a/src/PhpWord/Writer/ODText.php b/src/PhpWord/Writer/ODText.php
index 6d54706c8e..3eaf80ad4f 100644
--- a/src/PhpWord/Writer/ODText.php
+++ b/src/PhpWord/Writer/ODText.php
@@ -70,10 +70,8 @@ public function __construct(?PhpWord $phpWord = null)
 
     /**
      * Save PhpWord to file.
-     *
-     * @param string $filename
      */
-    public function save($filename = null): void
+    public function save(string $filename): void
     {
         $filename = $this->getTempFile($filename);
         $zip = $this->getZipArchive($filename);
diff --git a/src/PhpWord/Writer/RTF.php b/src/PhpWord/Writer/RTF.php
index ebbf8f56c0..1d89c03643 100644
--- a/src/PhpWord/Writer/RTF.php
+++ b/src/PhpWord/Writer/RTF.php
@@ -56,10 +56,8 @@ public function __construct(?PhpWord $phpWord = null)
 
     /**
      * Save content to file.
-     *
-     * @param string $filename
      */
-    public function save($filename = null): void
+    public function save(string $filename): void
     {
         $this->writeFile($this->openFile($filename), $this->getContent());
     }
diff --git a/src/PhpWord/Writer/Word2007.php b/src/PhpWord/Writer/Word2007.php
index ae10ba5a74..ab4fd1e3eb 100644
--- a/src/PhpWord/Writer/Word2007.php
+++ b/src/PhpWord/Writer/Word2007.php
@@ -91,10 +91,8 @@ public function __construct(?PhpWord $phpWord = null)
 
     /**
      * Save document by name.
-     *
-     * @param string $filename
      */
-    public function save($filename = null): void
+    public function save(string $filename): void
     {
         $filename = $this->getTempFile($filename);
         $zip = $this->getZipArchive($filename);