diff --git a/ext/dom/node.c b/ext/dom/node.c
index 88c058a6ac51..d54822d8077e 100644
--- a/ext/dom/node.c
+++ b/ext/dom/node.c
@@ -919,7 +919,7 @@ static bool dom_node_check_legacy_insertion_validity(xmlNodePtr parentp, xmlNode
 	}
 
 	/* Documents can never be a child. */
-	if (child->type == XML_DOCUMENT_NODE || child->type == XML_HTML_DOCUMENT_NODE) {
+	if (child->type == XML_DOCUMENT_NODE || child->type == XML_HTML_DOCUMENT_NODE || child->type == XML_NOTATION_NODE) {
 		php_dom_throw_error(HIERARCHY_REQUEST_ERR, stricterror);
 		return false;
 	}
diff --git a/ext/dom/parentnode/tree.c b/ext/dom/parentnode/tree.c
index aacc991cc735..5d068ee1bbd6 100644
--- a/ext/dom/parentnode/tree.c
+++ b/ext/dom/parentnode/tree.c
@@ -285,10 +285,10 @@ static bool dom_is_pre_insert_valid_without_step_1(php_libxml_ref_obj *document,
 		dom_hierarchy(parentNode, node) != SUCCESS
 		/* 4. If node is not a DocumentFragment, DocumentType, Element, or CharacterData node, then throw a "HierarchyRequestError" DOMException. */
 		|| node->type == XML_ATTRIBUTE_NODE
+		|| node->type == XML_NOTATION_NODE
 		|| (php_dom_follow_spec_doc_ref(document) && (
 			node->type == XML_ENTITY_REF_NODE
 			|| node->type == XML_ENTITY_NODE
-			|| node->type == XML_NOTATION_NODE
 			|| node->type == XML_DOCUMENT_NODE
 			|| node->type == XML_HTML_DOCUMENT_NODE
 			|| node->type >= XML_ELEMENT_DECL))) {
diff --git a/ext/dom/php_dom.c b/ext/dom/php_dom.c
index 0833d9a3c9be..e1d39f41bdc9 100644
--- a/ext/dom/php_dom.c
+++ b/ext/dom/php_dom.c
@@ -2629,6 +2629,13 @@ static xmlNodePtr dom_clone_helper(php_dom_libxml_ns_mapper *ns_mapper, xmlNodeP
 
 xmlNodePtr dom_clone_node(php_dom_libxml_ns_mapper *ns_mapper, xmlNodePtr node, xmlDocPtr doc, bool recursive)
 {
+	if (node->type == XML_NOTATION_NODE) {
+		const xmlEntity *notation = (const xmlEntity *) node;
+		xmlNodePtr clone = create_notation(NULL, notation->name, notation->ExternalID, notation->SystemID);
+		clone->doc = doc;
+		return clone;
+	}
+
 	if (node->type == XML_DTD_NODE) {
 		/* The behaviour w.r.t. the internal subset is implementation-defined according to DOM 3.
 		 * This follows what e.g. Java and C# do: copy it regardless of the recursiveness.
diff --git a/ext/dom/tests/gh25268_notation_insert.phpt b/ext/dom/tests/gh25268_notation_insert.phpt
new file mode 100644
index 000000000000..1db202a2e6d2
--- /dev/null
+++ b/ext/dom/tests/gh25268_notation_insert.phpt
@@ -0,0 +1,37 @@
+--TEST--
+GH-25268 (Inserting a DOMNotation clone into a legacy document)
+--EXTENSIONS--
+dom
+--FILE--
+<?php
+$doc = new DOMDocument();
+$doc->loadXML('<!DOCTYPE root [<!NOTATION GIF SYSTEM "image/gif">]><root><x/></root>');
+$notation = $doc->doctype->notations->getNamedItem('GIF');
+$root = $doc->documentElement;
+
+$tests = [
+    'appendChild' => fn() => $root->appendChild(clone $notation),
+    'insertBefore' => fn() => $root->insertBefore(clone $notation, $root->firstChild),
+    'replaceChild' => fn() => $root->replaceChild(clone $notation, $root->firstChild),
+    'append' => fn() => $root->append(clone $notation),
+    'append original' => fn() => $root->append($notation),
+];
+
+foreach ($tests as $name => $test) {
+    try {
+        $test();
+        echo $name, ': inserted', PHP_EOL;
+    } catch (DOMException $e) {
+        echo $name, ': ', $e::class, ': ', $e->getMessage(), PHP_EOL;
+    }
+}
+
+echo $doc->saveXML($root), PHP_EOL;
+?>
+--EXPECT--
+appendChild: DOMException: Hierarchy Request Error
+insertBefore: DOMException: Hierarchy Request Error
+replaceChild: DOMException: Hierarchy Request Error
+append: DOMException: Hierarchy Request Error
+append original: DOMException: Hierarchy Request Error
+<root><x/></root>
diff --git a/ext/dom/tests/modern/xml/gh25268_notation.phpt b/ext/dom/tests/modern/xml/gh25268_notation.phpt
new file mode 100644
index 000000000000..b535abf44166
--- /dev/null
+++ b/ext/dom/tests/modern/xml/gh25268_notation.phpt
@@ -0,0 +1,29 @@
+--TEST--
+GH-25268 (Cloning Dom\Notation loses its node)
+--EXTENSIONS--
+dom
+--CREDITS--
+YuanchengJiang
+--FILE--
+<?php
+$dom = Dom\XMLDocument::createFromString('<!DOCTYPE root [<!NOTATION GIF SYSTEM "image/gif">]><root/>');
+$notation = $dom->doctype->notations->getNamedItem("GIF");
+
+$clone = clone $notation;
+var_dump($clone->nodeName, $clone->ownerDocument === $dom, $clone->parentNode, $clone->isConnected);
+
+$clone2 = $notation->cloneNode();
+var_dump($clone2->nodeName, $clone2 === $clone);
+
+unset($dom, $notation);
+var_dump($clone->nodeName, $clone2->nodeName);
+?>
+--EXPECT--
+string(3) "GIF"
+bool(true)
+NULL
+bool(false)
+string(3) "GIF"
+bool(false)
+string(3) "GIF"
+string(3) "GIF"