diff --git a/app/test/crypto/identity_test.dart b/app/test/crypto/identity_test.dart
index e7b0ac5..02f7299 100644
--- a/app/test/crypto/identity_test.dart
+++ b/app/test/crypto/identity_test.dart
@@ -1,3 +1,5 @@
+// Needs the native libsignal library (FFI); skipped on builders without it (--exclude-tags ffi).
+@Tags(['ffi'])
 import 'dart:typed_data';
 
 import 'package:flutter_test/flutter_test.dart';
diff --git a/app/test/groups_admin_flow_test.dart b/app/test/groups_admin_flow_test.dart
index b4e2039..18ddba7 100644
--- a/app/test/groups_admin_flow_test.dart
+++ b/app/test/groups_admin_flow_test.dart
@@ -1,3 +1,5 @@
+// Needs the native libsignal library (FFI); skipped on builders without it (--exclude-tags ffi).
+@Tags(['ffi'])
 import 'dart:convert';
 import 'dart:io';
 import 'dart:math';
diff --git a/app/test/groups_security_test.dart b/app/test/groups_security_test.dart
index c4d4e50..cec4cf5 100644
--- a/app/test/groups_security_test.dart
+++ b/app/test/groups_security_test.dart
@@ -1,3 +1,5 @@
+// Needs the native libsignal library (FFI); skipped on builders without it (--exclude-tags ffi).
+@Tags(['ffi'])
 import 'dart:convert';
 import 'dart:io';
 import 'dart:math';
diff --git a/app/test/safety_number_test.dart b/app/test/safety_number_test.dart
index 4135051..1e890a1 100644
--- a/app/test/safety_number_test.dart
+++ b/app/test/safety_number_test.dart
@@ -1,3 +1,5 @@
+// Needs the native libsignal library (FFI); skipped on builders without it (--exclude-tags ffi).
+@Tags(['ffi'])
 import 'dart:typed_data';
 
 import 'package:flutter_test/flutter_test.dart';
diff --git a/app/test/storage/decoy_isolation_test.dart b/app/test/storage/decoy_isolation_test.dart
index da19f8d..a67cd05 100644
--- a/app/test/storage/decoy_isolation_test.dart
+++ b/app/test/storage/decoy_isolation_test.dart
@@ -1,3 +1,5 @@
+// Needs the native libsignal library (FFI); skipped on builders without it (--exclude-tags ffi).
+@Tags(['ffi'])
 // Argon2id (64 MiB) ×6 pod zátěží celé sady: víc než výchozích 30 s.
 @Timeout(Duration(minutes: 3))
 library;
diff --git a/app/test/storage/persistent_stores_test.dart b/app/test/storage/persistent_stores_test.dart
index 3eefd56..c66bba5 100644
--- a/app/test/storage/persistent_stores_test.dart
+++ b/app/test/storage/persistent_stores_test.dart
@@ -1,3 +1,5 @@
+// Needs the native libsignal library (FFI); skipped on builders without it (--exclude-tags ffi).
+@Tags(['ffi'])
 import 'dart:io';
 import 'dart:math';
 import 'dart:typed_data';