diff --git a/src/card/dtos/requests/fund-iban.request.dto.ts b/src/card/dtos/requests/fund-iban.request.dto.ts
index d22a544..66c2597 100644
--- a/src/card/dtos/requests/fund-iban.request.dto.ts
+++ b/src/card/dtos/requests/fund-iban.request.dto.ts
@@ -1,7 +1,9 @@
 import { ApiProperty } from '@nestjs/swagger';
+import { IsString } from 'class-validator';
 import { TransferToJuniorRequestDto } from '~/junior/dtos/request';
 
 export class FundIbanRequestDto extends TransferToJuniorRequestDto {
   @ApiProperty({ example: 'DE89370400440532013000' })
+  @IsString()
   iban!: string;
 }