diff --git a/index.js b/index.js
index 1ef5230..5229563 100644
--- a/index.js
+++ b/index.js
@@ -36,6 +36,7 @@ module.exports = function simpleSource(_options) {
 
 	return {
 		_promistreamVersion: 0,
+		_promistreamIsSource: true,
 		description: `simple source`,
 		peek: function peekValue_simpleSource() {
 			return Promise.try(() => {