diff --git a/source/basic.js b/source/basic.js
index a13b46e..792d67f 100644
--- a/source/basic.js
+++ b/source/basic.js
@@ -1,4 +1,7 @@
 ValidatorContext.prototype.validateBasic = function validateBasic(data, schema, dataPointerPath) {
+        if (data === undefined) {
+        	return null;
+        }
 	var error;
 	if (error = this.validateType(data, schema, dataPointerPath)) {
 		return error.prefixWith(null, "type");