diff --git a/tests/standalone/io/shared_socket_test.dart b/tests/standalone/io/shared_socket_test.dart
index 7f70a14..2fb755f 100644
--- a/tests/standalone/io/shared_socket_test.dart
+++ b/tests/standalone/io/shared_socket_test.dart
@@ -12,11 +12,18 @@
 import 'package:http/http.dart' as http;
 
 void main() async {
-  final workers = List<ServerWorker>.generate(4, (i) => ServerWorker(i));
-  workers.forEach((w) => w.start());
+  // Start a server to obtain a randomly assigned, free port.
+  final mainServer = await HttpServer.bind('::1', 0, shared: true);
+  final sharedPort = mainServer.port;
+
+  final workers =
+      List<ServerWorker>.generate(4, (i) => ServerWorker(i, sharedPort));
+  await Future.wait(workers.map((w) => w.start()));
+  mainServer.close();
+
   await Future.delayed(Duration(seconds: 1));
   // spawn client isolate
-  final clientisolate = await Isolate.spawn(client, 0);
+  final clientisolate = await Isolate.spawn(client, sharedPort);
   // Wait for 20 secs. It used to crash within 10 seconds.
   await Future.delayed(Duration(seconds: 20));
 
@@ -30,10 +37,11 @@
 
 class ServerWorker {
   final int workerid;
+  final int port;
   Isolate? _isolate;
   bool respawn = true;
 
-  ServerWorker(this.workerid);
+  ServerWorker(this.workerid, this.port);
 
   Future<void> start() async {
     final onExit = ReceivePort();
@@ -42,8 +50,10 @@
       // Respawn another isolate
       if (respawn) start();
     });
-    _isolate = await Isolate.spawn(_main, workerid,
+    final ready = ReceivePort();
+    _isolate = await Isolate.spawn(_main, [workerid, port, ready.sendPort],
         errorsAreFatal: true, onExit: onExit.sendPort);
+    await ready.first;
     if (workerid == 0) terminate();
   }
 
@@ -55,9 +65,13 @@
     });
   }
 
-  static _main(int workerid) async {
-    bool shared = true;
-    final server = await HttpServer.bind('::1', 1234, shared: shared);
+  static _main(List args) async {
+    final workerid = args[0] as int;
+    final port = args[1] as int;
+    final readyPort = args[2] as SendPort;
+
+    final server = await HttpServer.bind('::1', port, shared: true);
+    readyPort.send(null);
     server.listen((HttpRequest request) {
       print('from worker ${workerid}');
       final response = request.response;
@@ -77,12 +91,12 @@
   }
 }
 
-void client(int i) async {
+void client(int port) async {
   while (true) {
     final futures = <Future>[];
     final numAtOnce = 16; // enough to keep the server busy
     for (int i = 0; i < numAtOnce; ++i) {
-      futures.add(get('http://localhost:1234').then((_) {}));
+      futures.add(get('http://localhost:$port').then((_) {}));
     }
     await Future.wait(futures);
   }
diff --git a/tests/standalone_2/io/shared_socket_test.dart b/tests/standalone_2/io/shared_socket_test.dart
index 5f933bb..bd1a041 100644
--- a/tests/standalone_2/io/shared_socket_test.dart
+++ b/tests/standalone_2/io/shared_socket_test.dart
@@ -12,11 +12,18 @@
 import 'package:http/http.dart' as http;
 
 void main() async {
-  final workers = List<ServerWorker>.generate(4, (i) => ServerWorker(i));
-  workers.forEach((w) => w.start());
+  // Start a server to obtain a randomly assigned, free port.
+  final mainServer = await HttpServer.bind('::1', 0, shared: true);
+  final sharedPort = mainServer.port;
+
+  final workers =
+      List<ServerWorker>.generate(4, (i) => ServerWorker(i, sharedPort));
+  await Future.wait(workers.map((w) => w.start()));
+  mainServer.close();
+
   await Future.delayed(Duration(seconds: 1));
   // spawn client isolate
-  final clientisolate = await Isolate.spawn(client, 0);
+  final clientisolate = await Isolate.spawn(client, sharedPort);
   // Wait for 20 secs. It used to crash within 10 seconds.
   await Future.delayed(Duration(seconds: 20));
 
@@ -30,10 +37,11 @@
 
 class ServerWorker {
   final int workerid;
+  final int port;
   Isolate _isolate;
   bool respawn = true;
 
-  ServerWorker(this.workerid);
+  ServerWorker(this.workerid, this.port);
 
   Future<void> start() async {
     final onExit = ReceivePort();
@@ -42,8 +50,10 @@
       // Respawn another isolate
       if (respawn) start();
     });
-    _isolate = await Isolate.spawn(_main, workerid,
+    final ready = ReceivePort();
+    _isolate = await Isolate.spawn(_main, [workerid, port, ready.sendPort],
         errorsAreFatal: true, onExit: onExit.sendPort);
+    await ready.first;
     if (workerid == 0) terminate();
   }
 
@@ -57,9 +67,13 @@
     });
   }
 
-  static _main(int workerid) async {
-    bool shared = true;
-    final server = await HttpServer.bind('::1', 1234, shared: shared);
+  static _main(List args) async {
+    final workerid = args[0] as int;
+    final port = args[1] as int;
+    final readyPort = args[2] as SendPort;
+
+    final server = await HttpServer.bind('::1', port, shared: true);
+    readyPort.send(null);
     server.listen((HttpRequest request) {
       print('from worker ${workerid}');
       final response = request.response;
@@ -79,12 +93,12 @@
   }
 }
 
-void client(int i) async {
+void client(int port) async {
   while (true) {
     final futures = <Future>[];
     final numAtOnce = 16; // enough to keep the server busy
     for (int i = 0; i < numAtOnce; ++i) {
-      futures.add(get('http://localhost:1234').then((_) {}));
+      futures.add(get('http://localhost:$port').then((_) {}));
     }
     await Future.wait(futures);
   }
diff --git a/tools/VERSION b/tools/VERSION
index ff6e07f..51f1ac0 100644
--- a/tools/VERSION
+++ b/tools/VERSION
@@ -27,5 +27,5 @@
 MAJOR 2
 MINOR 12
 PATCH 0
-PRERELEASE 104
+PRERELEASE 105
 PRERELEASE_PATCH 0
\ No newline at end of file