diff --git a/packages/integrations/mdx/src/index.ts b/packages/integrations/mdx/src/index.ts
index 96f9af7d9e167..33e5994bd9bd0 100644
--- a/packages/integrations/mdx/src/index.ts
+++ b/packages/integrations/mdx/src/index.ts
@@ -129,7 +129,7 @@ export default function mdx(partialMdxOptions: Partial<MdxOptions> = {}): AstroI
 								name: '@astrojs/mdx-postprocess',
 								// These transforms must happen *after* JSX runtime transformations
 								transform(code, id) {
-									if (!id.endsWith('mdx')) return;
+									if (!id.endsWith('.mdx')) return;
 
 									const [moduleImports, moduleExports] = parseESM(code);