diff --git a/.changeset/eight-toes-pump.md b/.changeset/eight-toes-pump.md
new file mode 100644
index 0000000..bd89f98
--- /dev/null
+++ b/.changeset/eight-toes-pump.md
@@ -0,0 +1,5 @@
+---
+"microbundle": patch
+---
+
+Fix crash when traversing `"exports"` objects (#852)
diff --git a/src/index.js b/src/index.js
index ed1e3f6..7ad55a0 100644
--- a/src/index.js
+++ b/src/index.js
@@ -260,9 +260,12 @@ function replaceName(filename, name) {
 	);
 }
 
-function walk(exports) {
+function walk(exports, includeDefault) {
+	if (!exports) return null;
 	if (typeof exports === 'string') return exports;
-	return walk(exports['.'] || exports.import || exports.module);
+	let p = exports['.'] || exports.import || exports.module;
+	if (!p && includeDefault) p = exports.default;
+	return walk(p, includeDefault);
 }
 
 function getMain({ options, entry, format }) {
@@ -296,7 +299,7 @@ function getMain({ options, entry, format }) {
 		mainNoExtension,
 	);
 	mainsByFormat.modern = replaceName(
-		(pkg.exports && walk(pkg.exports)) ||
+		(pkg.exports && walk(pkg.exports, pkg.type === 'module')) ||
 			(pkg.syntax && pkg.syntax.esmodules) ||
 			pkg.esmodule ||
 			'x.modern.js',