diff --git a/qtism/common/dom/SerializableDomDocument.php b/qtism/common/dom/SerializableDomDocument.php
index a14cc9d5f..3ae55281d 100644
--- a/qtism/common/dom/SerializableDomDocument.php
+++ b/qtism/common/dom/SerializableDomDocument.php
@@ -23,19 +23,19 @@
 
 namespace qtism\common\dom;
 
+use DOMAttr;
+use DOMCDATASection;
+use DOMComment;
 use DOMDocument;
+use DOMDocumentFragment;
 use DOMDocumentType;
 use DOMElement;
-use DOMImplementation;
-use DOMDocumentFragment;
-use DOMComment;
-use DOMCDATASection;
-use DOMProcessingInstruction;
-use DOMText;
-use DOMAttr;
 use DOMEntityReference;
+use DOMImplementation;
 use DOMNode;
 use DOMNodeList;
+use DOMProcessingInstruction;
+use DOMText;
 use Error;
 
 /**
@@ -183,4 +183,9 @@ public function __unset(string $name): void
     {
         unset($this->dom->$name);
     }
+
+    public function getDom(): DOMDocument
+    {
+        return $this->dom;
+    }
 }
diff --git a/qtism/data/storage/xml/XmlDocument.php b/qtism/data/storage/xml/XmlDocument.php
index b1e4a7aaa..ed574b6a0 100644
--- a/qtism/data/storage/xml/XmlDocument.php
+++ b/qtism/data/storage/xml/XmlDocument.php
@@ -30,6 +30,7 @@
 use InvalidArgumentException;
 use LibXMLError;
 use LogicException;
+use qtism\common\dom\SerializableDomDocument;
 use qtism\common\utils\Url;
 use qtism\data\content\Flow;
 use qtism\data\QtiComponent;
@@ -59,7 +60,7 @@ class XmlDocument extends QtiDocument
      * The produced domDocument after a successful call to
      * XmlDocument::load or XmlDocument::save.
      *
-     * @var DOMDocument
+     * @var SerializableDomDocument
      */
     private $domDocument = null;
 
@@ -78,12 +79,17 @@ public function __construct($version = '2.1', QtiComponent $documentComponent =
         parent::__construct($version, $documentComponent);
     }
 
+    public function __toString(): string
+    {
+        return $this->saveToString(false);
+    }
+
     /**
-     * Set the DOMDocument object in use.
+     * Set the SerializableDomDocument object in use.
      *
-     * @param DOMDocument $domDocument A DOMDocument object.
+     * @param SerializableDomDocument $domDocument A DOMDocument object.
      */
-    protected function setDomDocument(DOMDocument $domDocument)
+    protected function setDomDocument(SerializableDomDocument $domDocument)
     {
         $this->domDocument = $domDocument;
     }
@@ -95,7 +101,7 @@ protected function setDomDocument(DOMDocument $domDocument)
      */
     public function getDomDocument()
     {
-        return $this->domDocument;
+        return $this->domDocument->getDom();
     }
 
     /**
@@ -137,7 +143,7 @@ public function loadFromString($string, $validate = false)
     protected function loadImplementation($data, $validate = false, $fromString = false)
     {
         try {
-            $this->setDomDocument(new DOMDocument('1.0', 'UTF-8'));
+            $this->setDomDocument(new SerializableDomDocument('1.0', 'UTF-8'));
             $this->getDomDocument()->preserveWhiteSpace = true;
 
             // Disable xml warnings and errors and fetch error information as needed.
@@ -260,7 +266,7 @@ protected function saveImplementation($uri = '', $formatOutput = true)
         $assessmentTest = $this->getDocumentComponent();
 
         if (!empty($assessmentTest)) {
-            $this->setDomDocument(new DOMDocument('1.0', 'UTF-8'));
+            $this->setDomDocument(new SerializableDomDocument('1.0', 'UTF-8'));
 
             if ($formatOutput == true) {
                 $this->getDomDocument()->formatOutput = true;
@@ -329,14 +335,14 @@ public function schemaValidate($filename = '')
         }
 
         $doc = $this->getDomDocument();
-        
+
         $oldErrorConfig = libxml_use_internal_errors(true);
         $valid = $doc->schemaValidate($filename);
 
         $libXmlErrors = libxml_get_errors();
         libxml_clear_errors();
         libxml_use_internal_errors($oldErrorConfig);
-        
+
         if (!$valid) {
             $formattedErrors = self::formatLibXmlErrors($libXmlErrors);
 
@@ -345,7 +351,7 @@ public function schemaValidate($filename = '')
                 realpath($filename),
                 $formattedErrors
             );
-            
+
             throw XmlStorageException::createValidationException($msg, $libXmlErrors);
         }
     }
diff --git a/test/qtismtest/data/storage/xml/XmlDocumentTest.php b/test/qtismtest/data/storage/xml/XmlDocumentTest.php
index ed77762c6..a25889c44 100644
--- a/test/qtismtest/data/storage/xml/XmlDocumentTest.php
+++ b/test/qtismtest/data/storage/xml/XmlDocumentTest.php
@@ -254,6 +254,35 @@ public function testLoadFromMalformedString()
         $doc->loadFromString('<assessmentItem>');
     }
 
+    public function testSerialization()
+    {
+        $doc = new XmlDocument('2.1');
+        $doc->loadFromString('<assessmentItemRef identifier="Q01" href="./Q01.xml"/>');
+
+        $this->assertEquals(
+            $doc->saveToString(),
+            unserialize(serialize($doc))->saveToString()
+        );
+    }
+
+    public function testOlderSerializedDataDeserialization()
+    {
+        if (PHP_VERSION_ID >= 80100 || PHP_VERSION_ID < 70400) {
+            $this->markTestSkipped('DOM objects serialization is impossible in PHP 8.1 or higher.');
+        }
+
+        $unserializedDoc = unserialize(file_get_contents(self::samplesDir(). 'serialized/xmldocument'));
+        $this->assertInstanceOf(XmlDocument::class, $unserializedDoc);
+
+        $doc = new XmlDocument('2.1');
+        $doc->loadFromString('<assessmentItemRef identifier="Q01" href="./Q01.xml"/>');
+
+        $this->assertEquals(
+            $doc->saveToString(),
+            $unserializedDoc->saveToString()
+        );
+    }
+
     public function testLoadNoVersion()
     {
         $doc = new XmlDocument('2.1');
diff --git a/test/samples/serialized/xmldocument b/test/samples/serialized/xmldocument
new file mode 100644
index 000000000..af85c18c0
Binary files /dev/null and b/test/samples/serialized/xmldocument differ