diff --git a/lib/cdp/websocket.go b/lib/cdp/websocket.go
index 2179cb90..911bcd92 100644
--- a/lib/cdp/websocket.go
+++ b/lib/cdp/websocket.go
@@ -35,6 +35,10 @@ type WebSocket struct {
 
 // Connect to browser
 func (ws *WebSocket) Connect(ctx context.Context, wsURL string, header http.Header) error {
+	if ws.conn != nil {
+		panic("duplicated connection: " + wsURL)
+	}
+
 	ctx, cancel := context.WithCancel(ctx)
 	ws.close = cancel
 
diff --git a/lib/cdp/websocket_test.go b/lib/cdp/websocket_test.go
index 7fb05882..8564b6bb 100644
--- a/lib/cdp/websocket_test.go
+++ b/lib/cdp/websocket_test.go
@@ -76,3 +76,17 @@ func (t T) newPage(ctx context.Context) (*cdp.Client, string) {
 
 	return client, sessionID
 }
+
+func (t T) DuplicatedConnectErr() {
+	l := launcher.New()
+	t.Cleanup(l.Kill)
+
+	u := l.MustLaunch()
+
+	ws := &cdp.WebSocket{}
+	t.E(ws.Connect(t.Context(), u, nil))
+
+	t.Panic(func() {
+		_ = ws.Connect(t.Context(), u, nil)
+	})
+}