diff --git a/stronglift_replacement/workout_app/lib/services/http_server_service.dart b/stronglift_replacement/workout_app/lib/services/http_server_service.dart
index d1ee043..5a2470b 100644
--- a/stronglift_replacement/workout_app/lib/services/http_server_service.dart
+++ b/stronglift_replacement/workout_app/lib/services/http_server_service.dart
@@ -26,6 +26,14 @@ class HttpServerService {
 
   HttpServer? _server;
 
+  /// Port [start] binds. Tests set 0 (ephemeral) so a host process that
+  /// already owns 8765 cannot make them fail or answer in our place.
+  @visibleForTesting
+  int port = kWorkoutServerPort;
+
+  /// The port actually bound, or null while stopped.
+  int? get boundPort => _server?.port;
+
   /// The most recent workout JSON string (updated after each finished workout).
   String? _latestJson;
 
@@ -53,16 +61,13 @@ class HttpServerService {
     if (_server != null) return; // already running
     await _loadFromDisk();
     try {
-      _server = await HttpServer.bind(
-        InternetAddress.anyIPv4,
-        kWorkoutServerPort,
-      );
+      _server = await HttpServer.bind(InternetAddress.anyIPv4, port);
       unawaited(_serve());
     } on SocketException catch (error) {
       // Port already in use or binding failed — not fatal.
       debugPrint(
         'WorkoutApp: could not bind the workout HTTP server on port '
-        '$kWorkoutServerPort ($error) — the PC cannot pull workouts over '
+        '$port ($error) — the PC cannot pull workouts over '
         'HTTP; ADB and sync still work.',
       );
       _server = null;
diff --git a/stronglift_replacement/workout_app/test/services/http_server_service_test.dart b/stronglift_replacement/workout_app/test/services/http_server_service_test.dart
index a0483b8..93c40ed 100644
--- a/stronglift_replacement/workout_app/test/services/http_server_service_test.dart
+++ b/stronglift_replacement/workout_app/test/services/http_server_service_test.dart
@@ -5,8 +5,11 @@ import 'package:workout_app/services/http_server_service.dart';
 
 void main() {
   group('HttpServerService', () {
+    // Ephemeral port: the host may already run something on 8765.
+    setUp(() => HttpServerService.instance.port = 0);
     tearDown(() async {
       await HttpServerService.instance.stop();
+      HttpServerService.instance.port = kWorkoutServerPort;
     });
 
     test('is a singleton', () {
@@ -44,22 +47,22 @@ void main() {
     });
 
     test('start swallows a bind failure when the port is taken', () async {
-      final blocker = await ServerSocket.bind(
-        InternetAddress.anyIPv4,
-        kWorkoutServerPort,
-      );
+      final blocker = await ServerSocket.bind(InternetAddress.anyIPv4, 0);
+      HttpServerService.instance.port = blocker.port;
       // Binding fails (SocketException) but start() must not throw.
       await HttpServerService.instance.start();
+      expect(HttpServerService.instance.boundPort, isNull);
       await blocker.close();
     });
 
     test('serves the latest workout over HTTP', () async {
       HttpServerService.instance.resetForTesting();
       await HttpServerService.instance.start();
+      final port = HttpServerService.instance.boundPort!;
       final client = HttpClient();
 
       Future<int> get(String path) async {
-        final req = await client.get('localhost', kWorkoutServerPort, path);
+        final req = await client.get('localhost', port, path);
         final resp = await req.close();
         await resp.drain<void>();
         return resp.statusCode;