diff --git a/packages/bundle-source/src/types.js b/packages/bundle-source/src/types.js
index ac2bf7be991..d5132df48a9 100644
--- a/packages/bundle-source/src/types.js
+++ b/packages/bundle-source/src/types.js
@@ -1,6 +1,10 @@
+/**
+ * @typedef {'getExport' | 'nestedEvaluate' | 'endoZipBase64'} ModuleFormat
+ */
+
 /**
  * @callback BundleSource
  * @param {string} startFilename - the filepath to start the bundling from
- * @param {string=} moduleFormat
+ * @param {ModuleFormat=} moduleFormat
  * @param {Object=} powers
  */