diff --git a/packages/socket.io-client/lib/socket.ts b/packages/socket.io-client/lib/socket.ts
index a1713a187b..1dc3239afa 100644
--- a/packages/socket.io-client/lib/socket.ts
+++ b/packages/socket.io-client/lib/socket.ts
@@ -111,9 +111,11 @@ export type DisconnectDescription =
       context?: unknown; // context should be typed as CloseEvent | XMLHttpRequest, but these types are not available on non-browser platforms
     };
 
+type ConnectError = Error & { data?: any };
+
 interface SocketReservedEvents {
   connect: () => void;
-  connect_error: (err: Error) => void;
+  connect_error: (err: ConnectError) => void;
   disconnect: (
     reason: Socket.DisconnectReason,
     description?: DisconnectDescription,
@@ -734,8 +736,7 @@ export class Socket<
 
       case PacketType.CONNECT_ERROR:
         this.destroy();
-        const err = new Error(packet.data.message);
-        // @ts-ignore
+        const err: ConnectError = new Error(packet.data.message);
         err.data = packet.data.data;
         this.emitReserved("connect_error", err);
         break;
diff --git a/packages/socket.io-client/test/socket.ts b/packages/socket.io-client/test/socket.ts
index 9374453850..6cdf8188c7 100644
--- a/packages/socket.io-client/test/socket.ts
+++ b/packages/socket.io-client/test/socket.ts
@@ -286,6 +286,17 @@ describe("socket", () => {
     });
   });
 
+  it("should forward the data attached to a middleware error", () => {
+    return wrap((done) => {
+      const socket = io(BASE_URL + "/no-with-data", { forceNew: true });
+      socket.on("connect_error", (err) => {
+        expect(err.data).to.eql({ code: "UNAUTHORIZED" });
+        socket.disconnect();
+        done();
+      });
+    });
+  });
+
   it("should not try to reconnect after a middleware failure", () => {
     return wrap((done) => {
       const socket = io(BASE_URL + "/no", {
diff --git a/packages/socket.io-client/test/support/server.ts b/packages/socket.io-client/test/support/server.ts
index 3003a6fea9..1a7f13736b 100644
--- a/packages/socket.io-client/test/support/server.ts
+++ b/packages/socket.io-client/test/support/server.ts
@@ -1,4 +1,4 @@
-import { Server } from "socket.io";
+import { ExtendedError, Server } from "socket.io";
 import expect = require("expect.js");
 
 export function createServer() {
@@ -44,6 +44,12 @@ export function createServer() {
     next(new Error("Auth failed (custom namespace)"));
   });
 
+  server.of("/no-with-data").use((socket, next) => {
+    const err: ExtendedError = new Error("Auth failed (with data)");
+    err.data = { code: "UNAUTHORIZED" };
+    next(err);
+  });
+
   server.on("connection", (socket) => {
     // simple test
     socket.on("hi", () => {
diff --git a/packages/socket.io-client/test/typed-events.test-d.ts b/packages/socket.io-client/test/typed-events.test-d.ts
index d7e56de46d..0f4efdf657 100644
--- a/packages/socket.io-client/test/typed-events.test-d.ts
+++ b/packages/socket.io-client/test/typed-events.test-d.ts
@@ -26,7 +26,7 @@ describe("typed events", () => {
         expectError(socket.on("connect", (arg) => {}));
 
         socket.on("connect_error", (err) => {
-          expectType<Error>(err);
+          expectType<Error & { data?: any }>(err);
         });
 
         socket.on("disconnect", (reason) => {