diff --git a/src/Render/PlainTextSitemapRender.php b/src/Render/PlainTextSitemapRender.php
index a965d2b..b361815 100644
--- a/src/Render/PlainTextSitemapRender.php
+++ b/src/Render/PlainTextSitemapRender.php
@@ -39,12 +39,12 @@ public function start(): string
                 ' xsi:schemaLocation="http://www.sitemaps.org/schemas/sitemap/0.9'.
                 ' http://www.sitemaps.org/schemas/sitemap/0.9/sitemap.xsd"'.
                 ' xmlns="http://www.sitemaps.org/schemas/sitemap/0.9"'.
-                ' xmlns:xhtml="https://www.w3.org/1999/xhtml"'.
+                ' xmlns:xhtml="http://www.w3.org/1999/xhtml"'.
                 '>';
         }
 
         return '<?xml version="1.0" encoding="utf-8"?>'.PHP_EOL.
-            '<urlset xmlns="http://www.sitemaps.org/schemas/sitemap/0.9" xmlns:xhtml="https://www.w3.org/1999/xhtml">';
+            '<urlset xmlns="http://www.sitemaps.org/schemas/sitemap/0.9" xmlns:xhtml="http://www.w3.org/1999/xhtml">';
     }
 
     /**
diff --git a/src/Render/XMLWriterSitemapRender.php b/src/Render/XMLWriterSitemapRender.php
index cd24fb8..1c2b868 100644
--- a/src/Render/XMLWriterSitemapRender.php
+++ b/src/Render/XMLWriterSitemapRender.php
@@ -64,7 +64,7 @@ public function start(): string
         }
 
         $this->writer->writeAttribute('xmlns', 'http://www.sitemaps.org/schemas/sitemap/0.9');
-        $this->writer->writeAttribute('xmlns:xhtml', 'https://www.w3.org/1999/xhtml');
+        $this->writer->writeAttribute('xmlns:xhtml', 'http://www.w3.org/1999/xhtml');
 
         // XMLWriter expects that we can add more attributes
         // we force XMLWriter to set the closing bracket ">"
diff --git a/tests/Render/PlainTextSitemapRenderTest.php b/tests/Render/PlainTextSitemapRenderTest.php
index 6ddcaa6..fd9b5a3 100644
--- a/tests/Render/PlainTextSitemapRenderTest.php
+++ b/tests/Render/PlainTextSitemapRenderTest.php
@@ -37,7 +37,7 @@ public function getValidating(): array
                 false,
                 '<urlset'.
                 ' xmlns="http://www.sitemaps.org/schemas/sitemap/0.9"'.
-                ' xmlns:xhtml="https://www.w3.org/1999/xhtml"'.
+                ' xmlns:xhtml="http://www.w3.org/1999/xhtml"'.
                 '>',
             ],
             [
@@ -47,7 +47,7 @@ public function getValidating(): array
                 ' xsi:schemaLocation="http://www.sitemaps.org/schemas/sitemap/0.9'.
                 ' http://www.sitemaps.org/schemas/sitemap/0.9/sitemap.xsd"'.
                 ' xmlns="http://www.sitemaps.org/schemas/sitemap/0.9"'.
-                ' xmlns:xhtml="https://www.w3.org/1999/xhtml"'.
+                ' xmlns:xhtml="http://www.w3.org/1999/xhtml"'.
                 '>',
             ],
         ];
diff --git a/tests/Render/XMLWriterSitemapRenderTest.php b/tests/Render/XMLWriterSitemapRenderTest.php
index fa284ba..ee9b690 100644
--- a/tests/Render/XMLWriterSitemapRenderTest.php
+++ b/tests/Render/XMLWriterSitemapRenderTest.php
@@ -42,7 +42,7 @@ public function getValidating(): array
                 false,
                 '<urlset'.
                 ' xmlns="http://www.sitemaps.org/schemas/sitemap/0.9"'.
-                ' xmlns:xhtml="https://www.w3.org/1999/xhtml"'.
+                ' xmlns:xhtml="http://www.w3.org/1999/xhtml"'.
                 '>',
             ],
             [
@@ -52,7 +52,7 @@ public function getValidating(): array
                 ' xsi:schemaLocation="http://www.sitemaps.org/schemas/sitemap/0.9'.
                 ' http://www.sitemaps.org/schemas/sitemap/0.9/sitemap.xsd"'.
                 ' xmlns="http://www.sitemaps.org/schemas/sitemap/0.9"'.
-                ' xmlns:xhtml="https://www.w3.org/1999/xhtml"'.
+                ' xmlns:xhtml="http://www.w3.org/1999/xhtml"'.
                 '>',
             ],
         ];