diff --git a/packages/astro/src/core/routing/manifest/create.ts b/packages/astro/src/core/routing/manifest/create.ts
index d1f498432e72..aabdd4e63d76 100644
--- a/packages/astro/src/core/routing/manifest/create.ts
+++ b/packages/astro/src/core/routing/manifest/create.ts
@@ -183,7 +183,7 @@ function createFileBasedRoutes(
 			validateSegment(segment, file);
 
 			const parts = getParts(segment, file);
-			const isIndex = isDir ? false : basename.startsWith('index.');
+			const isIndex = isDir ? false : basename.substring(0, basename.lastIndexOf('.')) === "index";
 			const routeSuffix = basename.slice(basename.indexOf('.'), -ext.length);
 			const isPage = validPageExtensions.has(ext);