diff --git a/src/global.ts b/src/global.ts
index 26105d1..20bc6b0 100644
--- a/src/global.ts
+++ b/src/global.ts
@@ -233,7 +233,7 @@ export function ctor() {
 }
 
 Array.prototype.random = function (this: Array<any>) {
-    return this[PublicShared.randomNum(0, this.length)];
+    return this[PublicShared.randomNum(0, this.length - 1)];
 };
 
 Array.prototype.intersection = function (this: Array<any>, other: Array<any>) {