diff --git a/NEWS b/NEWS
index 1cc265f02e8d..5ca7a0f6457c 100644
--- a/NEWS
+++ b/NEWS
@@ -27,6 +27,8 @@ PHP NEWS
that still have a live wrapper). (iliaal)
. Fixed a use-after-free when Dom\Element::setAttributeNS() replaces the
value of an attribute whose child still has a live wrapper. (iliaal)
+ . Fixed Dom\HTMLDocument::getElementById() not finding ids of SVG and
+ MathML elements. (Ilia Alshanetsky)
- GD:
. Fixed imageaffinematrixget() and imageaffinematrixconcat() reporting the
diff --git a/ext/dom/html5_parser.c b/ext/dom/html5_parser.c
index 34320a122f53..dbae8df5dbab 100644
--- a/ext/dom/html5_parser.c
+++ b/ext/dom/html5_parser.c
@@ -274,7 +274,7 @@ static lexbor_libxml2_bridge_status lexbor_libxml2_bridge_convert(
last_added_attr = lxml_attr;
/* xmlIsID does some other stuff too that is irrelevant here. */
- if (local_name_length == 2 && local_name[0] == 'i' && local_name[1] == 'd' && attr->node.ns == LXB_NS_HTML) {
+ if (local_name_length == 2 && local_name[0] == 'i' && local_name[1] == 'd' && lxml_attr->ns == NULL) {
if (xmlAddID(NULL, lxml_doc, value, lxml_attr) == 0) {
/* If the ID already exists, the ID attribute still needs to be marked as an ID. */
lxml_attr->atype = XML_ATTRIBUTE_ID;
diff --git a/ext/dom/tests/modern/html/parser/HTMLDocument_getElementById_foreign_namespaces.phpt b/ext/dom/tests/modern/html/parser/HTMLDocument_getElementById_foreign_namespaces.phpt
new file mode 100644
index 000000000000..d7bd611ff353
--- /dev/null
+++ b/ext/dom/tests/modern/html/parser/HTMLDocument_getElementById_foreign_namespaces.phpt
@@ -0,0 +1,38 @@
+--TEST--
+Dom\HTMLDocument::getElementById() finds ids of SVG and MathML elements
+--EXTENSIONS--
+dom
+--FILE--
+';
+$d = Dom\HTMLDocument::createFromString($html, LIBXML_NOERROR);
+var_dump([
+ 'svg #s' => $d->getElementById('s')?->tagName,
+ 'math #m' => $d->getElementById('m')?->tagName,
+ 'html #p' => $d->getElementById('p')?->tagName,
+ 'xml:id #r' => $d->getElementById('r')?->tagName,
+]);
+
+/* A fragment parsed into a foreign context inherits the context namespace, so
+ * this id really is namespaced and must not be registered. */
+$d2 = Dom\HTMLDocument::createEmpty();
+$z = $d2->createElementNS('http://www.w3.org/1999/xlink', 'z');
+$d2->appendChild($z);
+$z->innerHTML = '';
+$attr = $z->firstChild->attributes->item(0);
+var_dump($attr->localName, $attr->namespaceURI, $d2->getElementById('q'));
+?>
+--EXPECT--
+array(4) {
+ ["svg #s"]=>
+ string(3) "svg"
+ ["math #m"]=>
+ string(4) "math"
+ ["html #p"]=>
+ string(1) "P"
+ ["xml:id #r"]=>
+ NULL
+}
+string(2) "id"
+string(28) "http://www.w3.org/1999/xlink"
+NULL