diff --git a/src/tbank/tbank-connection.dto.ts b/src/tbank/tbank-connection.dto.ts
index d46f4f6..0b8d599 100644
--- a/src/tbank/tbank-connection.dto.ts
+++ b/src/tbank/tbank-connection.dto.ts
@@ -13,6 +13,6 @@ export class TbankConnectionStatusDto {
   @ApiProperty()
   connected: boolean;
 
-  @ApiProperty({ nullable: true, format: 'date-time' })
+  @ApiProperty({ type: String, nullable: true, format: 'date-time' })
   connectedAt: string | null;
 }