diff --git a/src/PhpSpreadsheet/Writer/Ods/WriterPart.php b/src/PhpSpreadsheet/Writer/Ods/WriterPart.php
index dee7532c..b07b38cb 100644
--- a/src/PhpSpreadsheet/Writer/Ods/WriterPart.php
+++ b/src/PhpSpreadsheet/Writer/Ods/WriterPart.php
@@ -24,6 +24,34 @@ namespace PhpOffice\PhpSpreadsheet\Writer\Ods;
  * @copyright  Copyright (c) 2006 - 2015 PhpSpreadsheet (https://github.com/PHPOffice/PhpSpreadsheet)
  * @license    http://www.gnu.org/licenses/old-licenses/lgpl-2.1.txt    LGPL
  */
-abstract class WriterPart extends \PhpOffice\PhpSpreadsheet\Writer\Xlsx\WriterPart
+abstract class WriterPart
 {
+    /**
+     * Parent Ods object.
+     *
+     * @var \PhpOffice\PhpSpreadsheet\Writer\Ods
+     */
+    private $parentWriter;
+
+    /**
+     * Get Ods writer.
+     *
+     * @throws \PhpOffice\PhpSpreadsheet\Writer\Exception
+     *
+     * @return \PhpOffice\PhpSpreadsheet\Writer\Ods
+     */
+    public function getParentWriter()
+    {
+        return $this->parentWriter;
+    }
+
+    /**
+     * Set parent Ods writer.
+     *
+     * @param \PhpOffice\PhpSpreadsheet\Writer\Ods $writer
+     */
+    public function __construct(\PhpOffice\PhpSpreadsheet\Writer\Ods $writer)
+    {
+        $this->parentWriter = $writer;
+    }
 }
diff --git a/src/PhpSpreadsheet/Writer/Xlsx/WriterPart.php b/src/PhpSpreadsheet/Writer/Xlsx/WriterPart.php
index 881683db..a743ab12 100644
--- a/src/PhpSpreadsheet/Writer/Xlsx/WriterPart.php
+++ b/src/PhpSpreadsheet/Writer/Xlsx/WriterPart.php
@@ -27,47 +27,30 @@ namespace PhpOffice\PhpSpreadsheet\Writer\Xlsx;
 abstract class WriterPart
 {
     /**
-     * Parent IWriter object.
+     * Parent Xlsx object.
      *
-     * @var \PhpOffice\PhpSpreadsheet\Writer\IWriter
+     * @var \PhpOffice\PhpSpreadsheet\Writer\Xlsx
      */
     private $parentWriter;
 
     /**
-     * Set parent IWriter object.
-     *
-     * @param \PhpOffice\PhpSpreadsheet\Writer\IWriter $pWriter
-     *
-     * @throws \PhpOffice\PhpSpreadsheet\Writer\Exception
-     */
-    public function setParentWriter(\PhpOffice\PhpSpreadsheet\Writer\IWriter $pWriter)
-    {
-        $this->parentWriter = $pWriter;
-    }
-
-    /**
-     * Get parent IWriter object.
+     * Get parent Xlsx object.
      *
      * @throws \PhpOffice\PhpSpreadsheet\Writer\Exception
      *
-     * @return \PhpOffice\PhpSpreadsheet\Writer\IWriter
+     * @return \PhpOffice\PhpSpreadsheet\Writer\Xlsx
      */
     public function getParentWriter()
     {
-        if (!is_null($this->parentWriter)) {
-            return $this->parentWriter;
-        }
-        throw new \PhpOffice\PhpSpreadsheet\Writer\Exception('No parent \\PhpOffice\\PhpSpreadsheet\\Writer\\IWriter assigned.');
+        return $this->parentWriter;
     }
 
     /**
-     * Set parent IWriter object.
+     * Set parent Xlsx object.
      *
-     * @param \PhpOffice\PhpSpreadsheet\Writer\IWriter $pWriter
-     *
-     * @throws \PhpOffice\PhpSpreadsheet\Writer\Exception
+     * @param \PhpOffice\PhpSpreadsheet\Writer\Xlsx $pWriter
      */
-    public function __construct(\PhpOffice\PhpSpreadsheet\Writer\IWriter $pWriter)
+    public function __construct(\PhpOffice\PhpSpreadsheet\Writer\Xlsx $pWriter)
     {
         $this->parentWriter = $pWriter;
     }