diff --git a/src/index.js b/src/index.js
index 7254eae..4d3290f 100644
--- a/src/index.js
+++ b/src/index.js
@@ -434,12 +434,15 @@ function createConfig(options, entry, format, writeMeta) {
 
 	let mainNoExtension = options.output;
 	if (options.multipleEntries) {
-		let name = entry.match(/([\\/])index(\.(umd|cjs|es|m))?\.m?js$/)
+		let name = entry.match(/([\\/])index(\.(umd|cjs|es|m))?\.(mjs|[tj]sx?)$/)
 			? mainNoExtension
 			: entry;
 		mainNoExtension = resolve(dirname(mainNoExtension), basename(name));
 	}
-	mainNoExtension = mainNoExtension.replace(/(\.(umd|cjs|es|m))?\.m?js$/, '');
+	mainNoExtension = mainNoExtension.replace(
+		/(\.(umd|cjs|es|m))?\.(mjs|[tj]sx?)$/,
+		'',
+	);
 
 	let moduleMain = replaceName(
 		pkg.module && !pkg.module.match(/src\//)