diff --git a/validators.js b/validators.js
index a9e9aec..243fec7 100644
--- a/validators.js
+++ b/validators.js
@@ -17,7 +17,7 @@ function validateString(value, name) {
 }
 
 function validateUnion(value, name, union) {
-  if (!union.includes(value)) {
+  if (!ArrayPrototypeIncludes(union, value)) {
     throw new ERR_INVALID_ARG_TYPE(name, `('${union.join('|')}')`, value);
   }
 }