diff --git a/lib/packages/wallet/eip712_signer.dart b/lib/packages/wallet/eip712_signer.dart
index f19f0e789..42a2591a1 100644
--- a/lib/packages/wallet/eip712_signer.dart
+++ b/lib/packages/wallet/eip712_signer.dart
@@ -24,11 +24,20 @@ class Eip712Signer {
     required bool swissTaxResidence,
     required String registrationDate,
   }) {
+    // The BitBox02 firmware refuses to sign typed data whose EIP712Domain has
+    // no chainId ("typed data has no chain ID" shown on the device), so
+    // hardware wallets sign with the chainId-extended domain. Software wallets
+    // keep the legacy chainId-less domain until Aktionariat has confirmed its
+    // signature re-verification accepts the extended variant — the API
+    // accepts both (pair PR DFXswiss/api#4354).
+    final includeChainIdInDomain = credentials is BitboxCredentials;
+
     final Map<String, dynamic> typedDataMap = {
       'types': {
         'EIP712Domain': [
           {'name': 'name', 'type': 'string'},
           {'name': 'version', 'type': 'string'},
+          if (includeChainIdInDomain) {'name': 'chainId', 'type': 'uint256'},
         ],
         'RealUnitUser': [
           {'name': 'email', 'type': 'string'},
@@ -47,7 +56,11 @@ class Eip712Signer {
         ],
       },
       'primaryType': 'RealUnitUser',
-      'domain': {'name': 'RealUnitUser', 'version': '1'},
+      'domain': {
+        'name': 'RealUnitUser',
+        'version': '1',
+        if (includeChainIdInDomain) 'chainId': chainId,
+      },
       'message': {
         'email': email,
         'name': name,
diff --git a/test/packages/wallet/eip712_signer_bitbox_test.dart b/test/packages/wallet/eip712_signer_bitbox_test.dart
index 438ccc787..c44cc1000 100644
--- a/test/packages/wallet/eip712_signer_bitbox_test.dart
+++ b/test/packages/wallet/eip712_signer_bitbox_test.dart
@@ -1,3 +1,4 @@
+import 'dart:convert';
 import 'dart:typed_data';
 
 import 'package:bitbox_flutter/bitbox_manager.dart';
@@ -48,6 +49,28 @@ void main() {
       expect(await signRegistration(), '0xcafebabe');
     });
 
+    // The BitBox02 firmware rejects typed data whose EIP712Domain has no
+    // chainId ("typed data has no chain ID" on the device) — hardware-wallet
+    // registrations must sign the chainId-extended domain. The software-wallet
+    // path keeps the legacy domain (pinned by the golden signature in
+    // eip712_signer_test.dart).
+    test('signs with the chainId-extended EIP-712 domain', () async {
+      when(
+        () => manager.signETHTypedMessage(any(), any(), any()),
+      ).thenAnswer((_) async => Uint8List.fromList([0x01]));
+
+      await signRegistration();
+
+      final jsonMessage =
+          verify(() => manager.signETHTypedMessage(any(), any(), captureAny())).captured.single as Uint8List;
+      final typedData = jsonDecode(utf8.decode(jsonMessage)) as Map<String, dynamic>;
+      expect(typedData['domain']['chainId'], 1);
+      expect(
+        (typedData['types']['EIP712Domain'] as List).map((e) => e['name']),
+        containsAll(['name', 'version', 'chainId']),
+      );
+    });
+
     test('throws SigningCancelledException on empty signature', () async {
       when(
         () => manager.signETHTypedMessage(any(), any(), any()),