diff --git a/index.js b/index.js
index bce1072..11764a2 100644
--- a/index.js
+++ b/index.js
@@ -3,6 +3,7 @@
 module.exports = function defineCombinator(callback) {
 	return {
 		callback: callback,
+		callIfNull: true,
 		___validatem_isSpecial: true,
 		___validatem_isCombinator: true,
 		___validatem_combinatorVersion: 1