diff --git a/internal/bot/bot.go b/internal/bot/bot.go
index d3b4ec5..e0d3738 100644
--- a/internal/bot/bot.go
+++ b/internal/bot/bot.go
@@ -28,11 +28,11 @@ const DisplayName = "calc"
 const Welcome = "Send me arithmetic, such as 2 + 2 or 5 * 5/2, " +
 	"and I will reply with the result."
 
-const (
-	// chatPort is where the chat client serves its API, on localhost
-	// inside the bot's own container.
-	chatPort = 5225
+// ChatPort is where the chat client serves its API, on localhost inside
+// the bot's own container.
+const ChatPort = 5225
 
+const (
 	// connectTimeout bounds the wait for a freshly started chat client
 	// to open its API, which includes creating or migrating the
 	// database.
@@ -54,12 +54,15 @@ const (
 
 var errExited = errors.New("simplex-chat exited")
 
-// Run starts the chat client with its database in cfg.DataDir, connects
-// to it, sets up the bot's address, then answers messages and serves the
-// API until ctx is cancelled — which is a clean stop and returns nil —
-// or until the chat client, the connection to it or the API's listener
-// fails, which returns the error.
-func Run(ctx context.Context, log *slog.Logger, cfg *config.Config) error {
+// Run starts the chat client with its database in cfg.DataDir, serving
+// its API on localhost at chatPort, connects to it, sets up the bot's
+// address, then answers messages and serves the bot's API until ctx is
+// cancelled — which is a clean stop and returns nil — or until the chat
+// client, the connection to it or the API's listener fails, which
+// returns the error.
+func Run(
+	ctx context.Context, log *slog.Logger, cfg *config.Config, chatPort int,
+) error {
 	err := os.MkdirAll(cfg.DataDir, dataDirMode)
 	if err != nil {
 		return fmt.Errorf("creating data directory: %w", err)
@@ -84,7 +87,7 @@ func Run(ctx context.Context, log *slog.Logger, cfg *config.Config) error {
 		<-cli.Done()
 	}()
 
-	client, err := connect(ctx, log, cli)
+	client, err := connect(ctx, log, cli, chatPort)
 	if err != nil {
 		return err
 	}
@@ -143,9 +146,10 @@ func stopAPI(ctx context.Context, log *slog.Logger, srv *http.Server) {
 	}
 }
 
-// connect waits for the chat client to open its API and connects to it.
+// connect waits for the chat client to open its API on chatPort and
+// connects to it.
 func connect(
-	ctx context.Context, log *slog.Logger, cli *simplex.CLI,
+	ctx context.Context, log *slog.Logger, cli *simplex.CLI, chatPort int,
 ) (*simplex.Client, error) {
 	ctx, cancel := context.WithTimeout(ctx, connectTimeout)
 	defer cancel()
diff --git a/internal/bot/run_test.go b/internal/bot/run_test.go
index a14620f..0c89299 100644
--- a/internal/bot/run_test.go
+++ b/internal/bot/run_test.go
@@ -52,9 +52,7 @@ func TestMain(m *testing.M) {
 // port it is given, on localhost, and answers the commands the bot
 // sends. SIGTERM ends it, as it ends the real client. Unlike the real
 // client, it also exits when the bot hangs up, so that it never
-// outlives a test run that was cut short. It takes port 5225, the chat
-// client's fixed port, so this test cannot run twice at once on one
-// machine.
+// outlives a test run that was cut short.
 func standIn() {
 	arg := func(name string) string {
 		return os.Args[slices.Index(os.Args, name)+1]
@@ -142,6 +140,8 @@ func TestStopDuringRequest(t *testing.T) {
 	t.Setenv("PATH", bin)
 
 	cfg := &config.Config{DataDir: t.TempDir(), Port: freePort(t), APIToken: credential}
+	// Never bot.ChatPort: a real chat client may be listening there.
+	chatPort := freePort(t)
 	ctx, stop := context.WithCancel(t.Context())
 	done := make(chan struct{})
 
@@ -150,7 +150,7 @@ func TestStopDuringRequest(t *testing.T) {
 	go func() {
 		defer close(done)
 
-		runErr = bot.Run(ctx, slog.New(slog.DiscardHandler), cfg)
+		runErr = bot.Run(ctx, slog.New(slog.DiscardHandler), cfg, chatPort)
 	}()
 
 	t.Cleanup(func() {
diff --git a/internal/cli/run.go b/internal/cli/run.go
index 8392856..a863fd2 100644
--- a/internal/cli/run.go
+++ b/internal/cli/run.go
@@ -45,7 +45,7 @@ func run(ctx context.Context, version string) error {
 	ctx, stop := signal.NotifyContext(ctx, syscall.SIGINT, syscall.SIGTERM)
 	defer stop()
 
-	err = bot.Run(ctx, log, cfg)
+	err = bot.Run(ctx, log, cfg, bot.ChatPort)
 	if err != nil {
 		log.Error("stopped", "error", err)