diff --git a/desktop/flipper-server-core/src/server/startServer.tsx b/desktop/flipper-server-core/src/server/startServer.tsx
index 8d89945c8..56f374c31 100644
--- a/desktop/flipper-server-core/src/server/startServer.tsx
+++ b/desktop/flipper-server-core/src/server/startServer.tsx
@@ -72,7 +72,17 @@ const verifyAuthToken = (req: http.IncomingMessage): boolean => {
   return true;
 };
 
+/**
+ * The following two variables are used to control when
+ * the server is ready to accept incoming connections.
+ * - isReady, is used to synchronously check if the server is
+ * ready or not.
+ * - isReadyWaitable achieves the same but is used by
+ * asynchronous functions which may want to wait until the
+ * server is ready.
+ */
 let isReady = false;
+let isReadyWaitable: Promise<void> | undefined;
 
 /**
  * Orchestrates the creation of the HTTP server, proxy, and WS server.
@@ -134,6 +144,17 @@ async function startHTTPServer(config: Config): Promise<{
 
   server.listen(config.port);
 
+  /**
+   * Create the promise which can be waited on. In this case,
+   * a reference to resolve is kept outside of the body of the promise
+   * so that other asynchronous functions can resolve the promise
+   * on its behalf.
+   */
+  let isReadyResolver: (value: void | PromiseLike<void>) => void;
+  isReadyWaitable = new Promise((resolve, _reject) => {
+    isReadyResolver = resolve;
+  });
+
   return new Promise((resolve) => {
     console.log(`Starting server on http://localhost:${config.port}`);
     const readyForIncomingConnections = (
@@ -141,11 +162,18 @@ async function startHTTPServer(config: Config): Promise<{
       companionEnv: FlipperServerCompanionEnv,
     ): Promise<void> => {
       attachSocketServer(socket, serverImpl, companionEnv);
+      /**
+       * At this point, the server is ready to accept incoming
+       * connections. Change the isReady state and resolve the
+       * promise so that other asychronous function become unblocked.
+       */
       isReady = true;
+      isReadyResolver();
       return new Promise((resolve) => {
         tracker.track('server-started', {
           port: config.port,
         });
+
         resolve();
       });
     };
@@ -214,8 +242,14 @@ function attachWS(server: http.Server, config: Config) {
   };
 
   const wss = new WebSocketServer(options);
-  server.on('upgrade', function upgrade(request, socket, head) {
-    const {pathname} = parse(request.url!);
+  server.on('upgrade', async function upgrade(request, socket, head) {
+    if (!request.url) {
+      console.log('[flipper-server] No request URL available');
+      socket.destroy();
+      return;
+    }
+
+    const {pathname} = parse(request.url);
 
     // Handled by Metro
     if (pathname === '/hot') {
@@ -223,13 +257,18 @@ function attachWS(server: http.Server, config: Config) {
     }
 
     if (pathname === '/') {
+      // Wait until the server is ready to accept incoming connections.
+      await isReadyWaitable;
       wss.handleUpgrade(request, socket, head, function done(ws) {
         wss.emit('connection', ws, request);
       });
       return;
     }
 
-    console.error('addWebsocket.upgrade -> unknown pathname', pathname);
+    console.error(
+      '[flipper-server] Unable to upgrade, unknown pathname',
+      pathname,
+    );
     socket.destroy();
   });