diff --git a/ext/dom/php_dom.c b/ext/dom/php_dom.c
index 9dc50ac28773d..58fe7b61c9417 100644
--- a/ext/dom/php_dom.c
+++ b/ext/dom/php_dom.c
@@ -1361,33 +1361,6 @@ void dom_normalize (xmlNodePtr nodep)
 }
 /* }}} end dom_normalize */
 
-
-/* {{{ void dom_set_old_ns(xmlDoc *doc, xmlNs *ns) */
-void dom_set_old_ns(xmlDoc *doc, xmlNs *ns) {
-	xmlNs *cur;
-
-	if (doc == NULL)
-		return;
-
-	if (doc->oldNs == NULL) {
-		doc->oldNs = (xmlNsPtr) xmlMalloc(sizeof(xmlNs));
-		if (doc->oldNs == NULL) {
-			return;
-		}
-		memset(doc->oldNs, 0, sizeof(xmlNs));
-		doc->oldNs->type = XML_LOCAL_NAMESPACE;
-		doc->oldNs->href = xmlStrdup(XML_XML_NAMESPACE);
-		doc->oldNs->prefix = xmlStrdup((const xmlChar *)"xml");
-	}
-
-	cur = doc->oldNs;
-	while (cur->next != NULL) {
-		cur = cur->next;
-	}
-	cur->next = ns;
-}
-/* }}} end dom_set_old_ns */
-
 void dom_reconcile_ns(xmlDocPtr doc, xmlNodePtr nodep) /* {{{ */
 {
 	xmlNsPtr nsptr, nsdftptr, curns, prevns = NULL;
@@ -1407,7 +1380,6 @@ void dom_reconcile_ns(xmlDocPtr doc, xmlNodePtr nodep) /* {{{ */
 						} else {
 							prevns->next = nsdftptr;
 						}
-						dom_set_old_ns(doc, curns);
 						curns = prevns;
 					}
 				}
diff --git a/ext/dom/php_dom.h b/ext/dom/php_dom.h
index 7a0a5e7d72e5f..abf88282dddfc 100644
--- a/ext/dom/php_dom.h
+++ b/ext/dom/php_dom.h
@@ -108,7 +108,6 @@ void php_dom_throw_error_with_message(int error_code, char *error_message, int s
 void node_list_unlink(xmlNodePtr node);
 int dom_check_qname(char *qname, char **localname, char **prefix, int uri_len, int name_len);
 xmlNsPtr dom_get_ns(xmlNodePtr node, char *uri, int *errorcode, char *prefix);
-void dom_set_old_ns(xmlDoc *doc, xmlNs *ns);
 void dom_reconcile_ns(xmlDocPtr doc, xmlNodePtr nodep);
 xmlNsPtr dom_get_nsdecl(xmlNode *node, xmlChar *localName);
 void dom_normalize (xmlNodePtr nodep);
diff --git a/ext/dom/tests/bug79700.phpt b/ext/dom/tests/bug79700.phpt
new file mode 100644
index 0000000000000..6977734054401
--- /dev/null
+++ b/ext/dom/tests/bug79700.phpt
@@ -0,0 +1,52 @@
+--TEST--
+dom: Can we go without dom_set_old_ns?
+--FILE--
+<?php
+
+$dom = new DOMDocument();
+$dom->appendChild($element = $dom->createElement('xml:xml'));
+$element->setAttribute('xmlns', 'http://www.w3.org/2000/xmlns/');
+$element->setAttribute('xmlns:xml', 'http://www.w3.org/XML/1998/namespace');
+echo $dom->saveXML();
+
+$html = new DOMDocument();
+$element->setAttribute('xmlns', 'http://www.w3.org/2000/xmlns/');
+$element->setAttribute('xmlns:xml', 'http://www.w3.org/XML/1998/namespace');
+$html->appendChild($element = $html->createElement('xml:html'));
+
+echo $html->saveHTML();
+
+$dom->documentElement->appendChild($dom->importNode($element));
+
+echo $dom->saveXML();
+
+// now test performance of 10000 namespaced elements. second run should not take more than 3x (safety margin) as long as first time.
+
+$dom = new DOMDocument();
+$root = $dom->createElementNS('http://www.w3.org/2000/xhtml', 'html');
+$dom->appendChild($root);
+
+$s = microtime(true);
+for ($i = 0; $i < 10000; $i++) {
+    $element = $dom->createElementNS('http://www.w3.org/2000/xhtml', 'p', 'Hello World');
+    $root->appendChild($element);
+}
+$firstRun = microtime(true) - $s;
+
+$s = microtime(true);
+for ($i = 0; $i < 10000; $i++) {
+    $element = $dom->createElementNS('http://www.w3.org/2000/xhtml', 'p', 'Hello World');
+    $root->appendChild($element);
+}
+$secondRun = microtime(true) - $s;
+
+if ($firstRun * 3 < $secondRun) {
+    echo "FAIL; second run took more than 3 times as long as first run. Performance should be linear\n";
+}
+
+--EXPECTF--
+<?xml version="1.0"?>
+<xml:xml xmlns="http://www.w3.org/2000/xmlns/" xmlns:xml="http://www.w3.org/XML/1998/namespace"/>
+<xml:html></xml:html>
+<?xml version="1.0"?>
+<xml:xml xmlns="http://www.w3.org/2000/xmlns/" xmlns:xml="http://www.w3.org/XML/1998/namespace"><xml:html/></xml:xml>