diff --git a/ui/src/api/gateway-browser-socket.test.ts b/ui/src/api/gateway-browser-socket.test.ts
index 2391e3d19f50..9809b0b93453 100644
--- a/ui/src/api/gateway-browser-socket.test.ts
+++ b/ui/src/api/gateway-browser-socket.test.ts
@@ -76,7 +76,20 @@ describe("createBrowserGatewaySocket", () => {
     socket?.emit("error");
     socket?.emit("close", { code: 1006, reason: "" });
     expect(handlers.error).toHaveBeenCalledOnce();
-    expect(handlers.close).toHaveBeenCalledWith(1006, "");
+    expect(handlers.close).toHaveBeenCalledWith(
+      1006,
+      `gateway websocket opening timed out after ${DEFAULT_PREAUTH_HANDSHAKE_TIMEOUT_MS}ms`,
+    );
+  });
+
+  it("preserves a real close reason when an opening timeout also occurred", async () => {
+    const handlers = createHandlers();
+    createBrowserGatewaySocket("wss://gateway.example", handlers);
+
+    await vi.advanceTimersByTimeAsync(DEFAULT_PREAUTH_HANDSHAKE_TIMEOUT_MS);
+    sockets[0]?.emit("close", { code: 1006, reason: "gateway supplied a close reason" });
+
+    expect(handlers.close).toHaveBeenCalledWith(1006, "gateway supplied a close reason");
   });
 
   it("clears the opening deadline after the socket opens", async () => {
diff --git a/ui/src/api/gateway-browser-socket.ts b/ui/src/api/gateway-browser-socket.ts
index 2efc0e55d0ca..e93c7f93ac37 100644
--- a/ui/src/api/gateway-browser-socket.ts
+++ b/ui/src/api/gateway-browser-socket.ts
@@ -10,7 +10,7 @@ export function createBrowserGatewaySocket(
 ): GatewayProtocolSocket {
   const socket = new WebSocket(url);
   let opening = true;
-  let openingTimedOut = false;
+  let openingTimeoutReason: string | undefined;
   let openingTimer: ReturnType<typeof setTimeout> | undefined;
   const finishOpening = () => {
     opening = false;
@@ -27,11 +27,12 @@ export function createBrowserGatewaySocket(
   socket.addEventListener("message", (event) => handlers.message(String(event.data ?? "")));
   socket.addEventListener("close", (event) => {
     finishOpening();
-    handlers.close(event.code, event.reason ?? "");
+    // Browsers erase locally initiated close reasons before the handshake finishes.
+    handlers.close(event.code, event.reason || openingTimeoutReason || "");
   });
   socket.addEventListener("error", () => {
     finishOpening();
-    if (!openingTimedOut) {
+    if (!openingTimeoutReason) {
       handlers.error(new Error("websocket error"));
     }
   });
@@ -44,13 +45,9 @@ export function createBrowserGatewaySocket(
       return;
     }
     opening = false;
-    openingTimedOut = true;
+    openingTimeoutReason = `gateway websocket opening timed out after ${DEFAULT_PREAUTH_HANDSHAKE_TIMEOUT_MS}ms`;
     try {
-      handlers.error(
-        new Error(
-          `gateway websocket opening timed out after ${DEFAULT_PREAUTH_HANDSHAKE_TIMEOUT_MS}ms`,
-        ),
-      );
+      handlers.error(new Error(openingTimeoutReason));
     } finally {
       socket.close();
     }