diff --git a/static_core/plugins/ets/stdlib/escompat/RegExp.ets b/static_core/plugins/ets/stdlib/escompat/RegExp.ets
index 7d176d9d27a492f211c9cce20c2213df5e20f88b..fe4b3245ca89be65d7f5345432d93ed268d6d6eb 100644
--- a/static_core/plugins/ets/stdlib/escompat/RegExp.ets
+++ b/static_core/plugins/ets/stdlib/escompat/RegExp.ets
@@ -1284,7 +1284,7 @@ export class RegExp extends Object {
             }
             let matchStr = result.$_get(0)
             if (matchStr == "") {
-                this.lastIndex = RegExp.advanceStringIndex(str, this.lastIndex, this.unicode)
+                this.lastIndex = RegExp.advanceStringIndex(str, this.lastIndex.toInt(), this.unicode)
             }
         }
         let lengthS = str.getLength()
@@ -1330,7 +1330,7 @@ export class RegExp extends Object {
             }
             let matchStr = result.$_get(0)
             if (matchStr == "") {
-                this.lastIndex = RegExp.advanceStringIndex(str, this.lastIndex, this.unicode)
+                this.lastIndex = RegExp.advanceStringIndex(str, this.lastIndex.toInt(), this.unicode)
             }
         }
         let lengthS = str.getLength()