diff --git a/src/utils/Utils.ts b/src/utils/Utils.ts
index 4387303d..09def620 100644
--- a/src/utils/Utils.ts
+++ b/src/utils/Utils.ts
@@ -102,7 +102,7 @@ export class Utils {
             throw new ReferenceError(`Cannot rotate empty string.`);
         }
 
-        for (let i = 0; i < times; i++) {
+        for (let i: number = 0; i < times; i++) {
             string = string[string.length - 1] + string.substring(0, string.length - 1);
         }