diff --git a/packages/integrations/sitemap/src/index.ts b/packages/integrations/sitemap/src/index.ts
index 057fc2371d..6b91246264 100644
--- a/packages/integrations/sitemap/src/index.ts
+++ b/packages/integrations/sitemap/src/index.ts
@@ -132,6 +132,18 @@ const createPlugin = (options?: SitemapOptions): AstroIntegration => {
 
 					pageUrls = Array.from(new Set([...pageUrls, ...routeUrls, ...(customPages ?? [])]));
 
+					if(config.build.format === 'file') {
+						pageUrls = pageUrls.map((url) => {
+
+							if(url.endsWith('/')) {
+								return url;
+							}
+
+							return url + '.html';
+
+						});
+					}
+
 					try {
 						if (filter) {
 							pageUrls = pageUrls.filter(filter);