diff -r 5ca9b0d569a5 -r a9ecbf6ad7ed src/pyams_default_theme/features/sitemap/templates/root-sitemap.pt
--- a/src/pyams_default_theme/features/sitemap/templates/root-sitemap.pt	Wed Jan 09 10:18:00 2019 +0100
+++ b/src/pyams_default_theme/features/sitemap/templates/root-sitemap.pt	Wed Jan 09 10:18:36 2019 +0100
@@ -2,7 +2,7 @@
 <sitemapindex xmlns="http://www.sitemaps.org/schemas/sitemap/0.9">
 	<tal:loop repeat="(ts, source) view.sources">
 		<sitemap>
-			<loc>${tales:absolute_url(source)}/sitemap.xml</loc>
+			<loc tal:define="source_url tales:absolute_url(source)">${source_url.replace('+', '%2B')}/sitemap.xml</loc>
 			<lastmod>${ts}</lastmod>
 		</sitemap>
 	</tal:loop>