diff --git a/NEWS b/NEWS
index c693d601c8d..13d668b7665 100644
--- a/NEWS
+++ b/NEWS
@@ -17,6 +17,9 @@ PHP                                                                        NEWS
   . Fixed bug GH-11997 (ctype_alnum 5 times slower in PHP 8.1 or greater).
     (nielsdos)
 
+- DOM:
+  . Restore old namespace reconciliation behaviour. (nielsdos)
+
 - Filter:
   . Fix explicit FILTER_REQUIRE_SCALAR with FILTER_CALLBACK (ilutov)
 
diff --git a/ext/dom/php_dom.c b/ext/dom/php_dom.c
index bada817e301..468d9345880 100644
--- a/ext/dom/php_dom.c
+++ b/ext/dom/php_dom.c
@@ -1465,11 +1465,16 @@ static void dom_reconcile_ns_internal(xmlDocPtr doc, xmlNodePtr nodep, xmlNodePt
 
 static void dom_libxml_reconcile_ensure_namespaces_are_declared(xmlNodePtr nodep)
 {
+	/* Ideally we'd use the DOM-wrapped version, but we cannot: https://github.com/php/php-src/pull/12308. */
+#if 0
 	/* Put on stack to avoid allocation.
 	 * Although libxml2 currently does not use this for the reconciliation, it still
 	 * makes sense to do this just in case libxml2's internal change in the future. */
 	xmlDOMWrapCtxt dummy_ctxt = {0};
 	xmlDOMWrapReconcileNamespaces(&dummy_ctxt, nodep, /* options */ 0);
+#else
+	xmlReconciliateNs(nodep->doc, nodep);
+#endif
 }
 
 void dom_reconcile_ns(xmlDocPtr doc, xmlNodePtr nodep) /* {{{ */
diff --git a/ext/dom/tests/DOMElement_toggleAttribute.phpt b/ext/dom/tests/DOMElement_toggleAttribute.phpt
index ed29be899da..a5a1ac5dd1e 100644
--- a/ext/dom/tests/DOMElement_toggleAttribute.phpt
+++ b/ext/dom/tests/DOMElement_toggleAttribute.phpt
@@ -123,26 +123,26 @@ bool(true)
 Toggling namespaces:
 bool(false)
 <?xml version="1.0"?>
-<container xmlns:foo="some:ns2" xmlns:anotherone="some:ns3" xmlns="some:ns"><foo:bar/><baz/></container>
+<default:container xmlns:foo="some:ns2" xmlns:anotherone="some:ns3" xmlns:default="some:ns"><foo:bar/><default:baz/></default:container>
 bool(false)
 <?xml version="1.0"?>
-<container xmlns:foo="some:ns2" xmlns="some:ns"><foo:bar/><baz/></container>
+<default:container xmlns:foo="some:ns2" xmlns:default="some:ns"><foo:bar/><default:baz/></default:container>
 bool(true)
 <?xml version="1.0"?>
-<container xmlns:foo="some:ns2" xmlns="some:ns" xmlns:anotherone=""><foo:bar/><baz/></container>
+<default:container xmlns:foo="some:ns2" xmlns:default="some:ns" xmlns:anotherone=""><foo:bar/><default:baz/></default:container>
 bool(false)
 <?xml version="1.0"?>
-<container xmlns="some:ns" xmlns:anotherone=""><foo:bar xmlns:foo="some:ns2"/><baz/></container>
+<default:container xmlns:default="some:ns" xmlns:anotherone="" xmlns:foo="some:ns2"><foo:bar/><default:baz/></default:container>
 bool(false)
 <?xml version="1.0"?>
-<container xmlns="some:ns" xmlns:anotherone=""><foo:bar xmlns:foo="some:ns2"/><baz/></container>
+<default:container xmlns:default="some:ns" xmlns:anotherone="" xmlns:foo="some:ns2"><foo:bar/><default:baz/></default:container>
 Toggling namespaced attributes:
 bool(true)
 bool(true)
 bool(true)
 bool(false)
 <?xml version="1.0"?>
-<container xmlns="some:ns" xmlns:anotherone="" test:test=""><foo:bar xmlns:foo="some:ns2" foo:test="" doesnotexist:test=""/><baz/></container>
+<default:container xmlns:default="some:ns" xmlns:anotherone="" xmlns:foo="some:ns2" test:test=""><foo:bar foo:test="" doesnotexist:test=""/><default:baz/></default:container>
 namespace of test:test = NULL
 namespace of foo:test = string(8) "some:ns2"
 namespace of doesnotexist:test = NULL
@@ -153,6 +153,6 @@ bool(false)
 bool(true)
 bool(false)
 <?xml version="1.0"?>
-<container xmlns="some:ns" xmlns:anotherone=""><foo:bar xmlns:foo="some:ns2" doesnotexist:test2=""/><baz/></container>
+<default:container xmlns:default="some:ns" xmlns:anotherone="" xmlns:foo="some:ns2"><foo:bar doesnotexist:test2=""/><default:baz/></default:container>
 Checking toggled namespace:
 string(0) ""
diff --git a/ext/dom/tests/bug47530.phpt b/ext/dom/tests/bug47530.phpt
index 0fb990e0e7b..301a418fbe8 100644
--- a/ext/dom/tests/bug47530.phpt
+++ b/ext/dom/tests/bug47530.phpt
@@ -118,18 +118,18 @@ test_appendChild_with_shadowing();
 --EXPECT--
 -- Test document fragment with import --
 <?xml version="1.0"?>
-<html xmlns="https://php.net/something" xmlns:ns="https://php.net/whatever"><element ns:foo="https://php.net/bar"/></html>
+<html xmlns="https://php.net/something" xmlns:ns="https://php.net/whatever"><default:element xmlns:default="https://php.net/something" ns:foo="https://php.net/bar"/></html>
 -- Test document fragment without import --
 <?xml version="1.0"?>
-<html xmlns=""><element xmlns:foo="https://php.net/bar"><foo:bar/><bar xmlns=""/></element></html>
+<html xmlns=""><element xmlns:foo="https://php.net/bar"><foo:bar/><bar/></element></html>
 string(7) "foo:bar"
 string(19) "https://php.net/bar"
 -- Test document import --
 <?xml version="1.0"?>
-<feed xmlns="http://www.w3.org/2005/Atom">
-<div xmlns="http://www.w3.org/1999/xhtml">
-    <p>Test-Text</p>
-</div>
+<feed xmlns="http://www.w3.org/2005/Atom" xmlns:default="http://www.w3.org/1999/xhtml">
+<default:div xmlns="http://www.w3.org/1999/xhtml">
+    <default:p>Test-Text</default:p>
+</default:div>
 </feed>
 -- Test partial document import --
 <?xml version="1.0"?>
diff --git a/ext/dom/tests/bug47847.phpt b/ext/dom/tests/bug47847.phpt
index 324bf9508d5..1c9ec95418e 100644
--- a/ext/dom/tests/bug47847.phpt
+++ b/ext/dom/tests/bug47847.phpt
@@ -2,6 +2,8 @@
 Bug #47847 (importNode loses the namespace of an XML element)
 --EXTENSIONS--
 dom
+--XFAIL--
+See https://github.com/php/php-src/pull/12308
 --FILE--
 <?php
 $fromdom = new DOMDocument();
diff --git a/ext/dom/tests/bug55294.phpt b/ext/dom/tests/bug55294.phpt
index 19534955029..eb198a78dde 100644
--- a/ext/dom/tests/bug55294.phpt
+++ b/ext/dom/tests/bug55294.phpt
@@ -2,6 +2,8 @@
 Bug #55294 (DOMDocument::importNode shifts namespaces when "default" namespace exists)
 --EXTENSIONS--
 dom
+--XFAIL--
+See https://github.com/php/php-src/pull/12308
 --FILE--
 <?php
 
diff --git a/ext/dom/tests/delayed_freeing/gh9628_1.phpt b/ext/dom/tests/delayed_freeing/gh9628_1.phpt
index 0c32778d6ce..18d754ae217 100644
--- a/ext/dom/tests/delayed_freeing/gh9628_1.phpt
+++ b/ext/dom/tests/delayed_freeing/gh9628_1.phpt
@@ -43,6 +43,6 @@ string(7) "some:ns"
 <span xmlns:test="some:ns2" xmlns="some:ns" id="1">
         
     </span>
-<span xmlns="some:ns" id="2">Test <test:test xmlns:test="some:ns2"/></span>
+<default:span xmlns:default="some:ns" xmlns:test="some:ns2" id="2">Test <test:test/></default:span>
 string(1) "2"
 string(7) "some:ns"
diff --git a/ext/dom/tests/specific_namespace_behaviour.phpt b/ext/dom/tests/specific_namespace_behaviour.phpt
new file mode 100644
index 00000000000..e6499e6ba52
--- /dev/null
+++ b/ext/dom/tests/specific_namespace_behaviour.phpt
@@ -0,0 +1,27 @@
+--TEST--
+DOM: specific namespace behaviour for applications with fixed serialization requirements
+--EXTENSIONS--
+dom
+--FILE--
+<?php
+
+$dom1 = new DOMDocument();
+$dom1->loadXML(<<<XML
+<wsse:Security xmlns:wsse="foo:bar">
+    <ds:Signature xmlns:ds="http://www.w3.org/2000/09/xmldsig#">
+    </ds:Signature>
+</wsse:Security>
+XML);
+$dom2 = new DOMDocument();
+$dom2->loadXML('<xml><child/></xml>');
+$wsse = $dom2->importNode($dom1->documentElement, true);
+$dom2->firstChild->firstChild->appendChild($wsse);
+echo $dom2->saveXML();
+
+?>
+--EXPECT--
+<?xml version="1.0"?>
+<xml><child><wsse:Security xmlns:wsse="foo:bar" xmlns:ds="http://www.w3.org/2000/09/xmldsig#">
+    <ds:Signature xmlns:ds="http://www.w3.org/2000/09/xmldsig#">
+    </ds:Signature>
+</wsse:Security></child></xml>
diff --git a/ext/libxml/libxml.c b/ext/libxml/libxml.c
index 8529a0c609c..6b9cd64c299 100644
--- a/ext/libxml/libxml.c
+++ b/ext/libxml/libxml.c
@@ -301,8 +301,13 @@ PHP_LIBXML_API void php_libxml_node_free_list(xmlNodePtr node)
 				if (curnode->type == XML_ELEMENT_NODE) {
 					/* This ensures that namespace references in this subtree are defined within this subtree,
 					 * otherwise a use-after-free would be possible when the original namespace holder gets freed. */
+#if 0
 					xmlDOMWrapCtxt dummy_ctxt = {0};
 					xmlDOMWrapReconcileNamespaces(&dummy_ctxt, curnode, /* options */ 0);
+#else
+					/* See php_dom.c */
+					xmlReconciliateNs(curnode->doc, curnode);
+#endif
 				}
 				/* Skip freeing */
 				curnode = next;