diff --git a/Userland/Libraries/LibWeb/DOM/NamedNodeMap.cpp b/Userland/Libraries/LibWeb/DOM/NamedNodeMap.cpp
index f0a4d41a06..8d2102de5a 100644
--- a/Userland/Libraries/LibWeb/DOM/NamedNodeMap.cpp
+++ b/Userland/Libraries/LibWeb/DOM/NamedNodeMap.cpp
@@ -92,6 +92,12 @@ WebIDL::ExceptionOr<Attr const*> NamedNodeMap::set_named_item(Attr& attribute)
     return set_attribute(attribute);
 }
 
+// https://dom.spec.whatwg.org/#dom-namednodemap-setnameditemns
+WebIDL::ExceptionOr<Attr const*> NamedNodeMap::set_named_item_ns(Attr& attribute)
+{
+    return set_attribute(attribute);
+}
+
 // https://dom.spec.whatwg.org/#dom-namednodemap-removenameditem
 WebIDL::ExceptionOr<Attr const*> NamedNodeMap::remove_named_item(StringView qualified_name)
 {
diff --git a/Userland/Libraries/LibWeb/DOM/NamedNodeMap.h b/Userland/Libraries/LibWeb/DOM/NamedNodeMap.h
index 566a584ebd..e8ccfad02e 100644
--- a/Userland/Libraries/LibWeb/DOM/NamedNodeMap.h
+++ b/Userland/Libraries/LibWeb/DOM/NamedNodeMap.h
@@ -38,6 +38,7 @@ public:
     Attr const* get_named_item(StringView qualified_name) const;
     Attr const* get_named_item_ns(StringView namespace_, StringView local_name) const;
     WebIDL::ExceptionOr<Attr const*> set_named_item(Attr& attribute);
+    WebIDL::ExceptionOr<Attr const*> set_named_item_ns(Attr& attribute);
     WebIDL::ExceptionOr<Attr const*> remove_named_item(StringView qualified_name);
     WebIDL::ExceptionOr<Attr const*> remove_named_item_ns(StringView namespace_, StringView local_name);
 
diff --git a/Userland/Libraries/LibWeb/DOM/NamedNodeMap.idl b/Userland/Libraries/LibWeb/DOM/NamedNodeMap.idl
index af50fb2511..cf52b16552 100644
--- a/Userland/Libraries/LibWeb/DOM/NamedNodeMap.idl
+++ b/Userland/Libraries/LibWeb/DOM/NamedNodeMap.idl
@@ -9,7 +9,7 @@ interface NamedNodeMap {
     Attr? getNamedItemNS(DOMString? namespace, DOMString localName);
 
     [CEReactions] Attr? setNamedItem(Attr attr);
-    // [CEReactions] Attr? setNamedItemNS(Attr attr);
+    [CEReactions] Attr? setNamedItemNS(Attr attr);
 
     [CEReactions] Attr removeNamedItem(DOMString qualifiedName);
     [CEReactions] Attr removeNamedItemNS(DOMString? namespace, DOMString localName);