diff --git a/app/views/public/api/v1/portals/sitemap.xml.erb b/app/views/public/api/v1/portals/sitemap.xml.erb
index d3e2b8301..1ea828165 100644
--- a/app/views/public/api/v1/portals/sitemap.xml.erb
+++ b/app/views/public/api/v1/portals/sitemap.xml.erb
@@ -1,9 +1,9 @@
 <?xml version="1.0" encoding="UTF-8"?>
-<sitemapindex>
+<urlset xmlns="http://www.sitemaps.org/schemas/sitemap/0.9">
   <% @portal.articles.where(status: :published).each do |article| %>
-    <sitemap>
+    <url>
       <loc><%= @help_center_url %><%= generate_article_link(@portal.slug, article.slug, false, false) %></loc>
-      <lastmod><%= article.updated_at.strftime("%Y-%m-%d") %></lastmod>
-    </sitemap>
+      <lastmod><%= article.updated_at.to_date.iso8601 %></lastmod>
+    </url>
   <% end %>
-</sitemapindex>
\ No newline at end of file
+</urlset>
diff --git a/spec/controllers/public/api/v1/portals_controller_spec.rb b/spec/controllers/public/api/v1/portals_controller_spec.rb
index 92ab56e5b..9cc77a19c 100644
--- a/spec/controllers/public/api/v1/portals_controller_spec.rb
+++ b/spec/controllers/public/api/v1/portals_controller_spec.rb
@@ -60,24 +60,35 @@ RSpec.describe Public::Api::V1::PortalsController, type: :request do
 
   describe 'GET /public/api/v1/portals/{portal_slug}/sitemap' do
     context 'when custom_domain is present' do
-      it 'gets a valid sitemap' do
+      it 'returns a valid urlset sitemap with the correct namespace' do
         get "/hc/#{portal.slug}/sitemap.xml"
+
         expect(response).to have_http_status(:success)
-        expect(response.body).to match(/<sitemap/)
-        expect(Nokogiri::XML(response.body).errors).to be_empty
+
+        doc = Nokogiri::XML(response.body)
+        expect(doc.errors).to be_empty
+
+        expect(doc.root.name).to eq('urlset')
+        expect(doc.root.namespace&.href).to eq('http://www.sitemaps.org/schemas/sitemap/0.9')
       end
 
-      it 'has valid sitemap links' do
+      it 'contains valid article URLs for the portal' do
         get "/hc/#{portal.slug}/sitemap.xml"
+
         expect(response).to have_http_status(:success)
-        parsed_xml = Nokogiri::XML(response.body)
-        links = parsed_xml.css('loc')
 
-        links.each do |link|
-          expect(link.text).to match(%r{https://www\.example\.com/hc/test-portal/articles/\d+})
-        end
+        doc = Nokogiri::XML(response.body)
+        doc.remove_namespaces!
 
-        expect(links.length).to eq 3
+        # ensure we are NOT returning a sitemapindex
+        expect(doc.xpath('//sitemapindex')).to be_empty
+
+        links = doc.xpath('//url/loc').map(&:text)
+        expect(links.length).to eq(3)
+
+        expect(links).to all(
+          match(%r{\Ahttps://www\.example\.com/hc/#{Regexp.escape(portal.slug)}/articles/\d+})
+        )
       end
     end
   end