diff --git a/test/test_websocket.py b/test/test_websocket.py
index fcbcedb..ebebbcb 100644
--- a/test/test_websocket.py
+++ b/test/test_websocket.py
@@ -122,6 +122,7 @@ class WebSocketServer:
         # that the asyncio server thread has finished startup.
         self._server_started_event = threading.Event()
         self._server_thread = threading.Thread(target=self._run_server_thread)
+        self._current_connection = None
 
     def __enter__(self):
         # main thread is entering the `with` block: start the server...
@@ -179,6 +180,13 @@ class WebSocketServer:
             self._current_connection = None
 
     def send_async(self, msg):
+        # Wait for a connection to be established before trying to send
+        max_wait = time() + TIMEOUT
+        while self._current_connection is None:
+            if time() > max_wait:
+                raise RuntimeError("Timeout waiting for WebSocket connection to be established")
+            sleep(0.01)
+
         asyncio.run_coroutine_threadsafe(self._current_connection.send(msg), self._server_loop)