diff --git a/assets/js/phoenix/longpoll.js b/assets/js/phoenix/longpoll.js
index 2ee739fac3..cc9c1d20fc 100644
--- a/assets/js/phoenix/longpoll.js
+++ b/assets/js/phoenix/longpoll.js
@@ -71,6 +71,13 @@ export default class LongPoll {
     this.ajax("GET", headers, null, () => this.ontimeout(), resp => {
       if(resp){
         var {status, token, messages} = resp
+        if(status === 410 && this.token !== null){
+          // In case we already have a token, this means that our existing session
+          // is gone. We fail so that the client rejoins its channels.
+          this.onerror(410)
+          this.closeAndRetry(3410, "session_gone", false)
+          return
+        }
         this.token = token
       } else {
         status = 0
diff --git a/assets/test/longpoll_test.js b/assets/test/longpoll_test.js
index f02871a39f..4f190e1d77 100644
--- a/assets/test/longpoll_test.js
+++ b/assets/test/longpoll_test.js
@@ -83,11 +83,11 @@ describe("LongPoll", () => {
       const authToken = "my-auth-token"
       const encodedToken = btoa(authToken)
       const protocols = ["phoenix", `${AUTH_TOKEN_PREFIX}${encodedToken}`]
-      
+
       const longpoll = new LongPoll("http://localhost/socket/longpoll", protocols)
       longpoll.timeout = 1000
       longpoll.poll()
-      
+
       // Verify Ajax.request was called with the correct headers
       expect(Ajax.request).toHaveBeenCalledWith(
         "GET",
@@ -104,7 +104,7 @@ describe("LongPoll", () => {
       const longpoll = new LongPoll("http://localhost/socket/longpoll", undefined)
       longpoll.timeout = 1000
       longpoll.poll()
-      
+
       // Verify Ajax.request was called without auth token header
       expect(Ajax.request).toHaveBeenCalledWith(
         "GET",
@@ -116,6 +116,27 @@ describe("LongPoll", () => {
         expect.any(Function)
       )
     })
+
+    it("should treat 410 as error when token already exists", () => {
+      const longpoll = new LongPoll("http://localhost/socket/longpoll", undefined)
+      longpoll.timeout = 1000
+      longpoll.token = "existing-token"
+
+      const mockOnerror = jest.fn()
+      const mockCloseAndRetry = jest.fn()
+      longpoll.onerror = mockOnerror
+      longpoll.closeAndRetry = mockCloseAndRetry
+
+      Ajax.request.mockImplementation((method, url, headers, body, timeout, ontimeout, callback) => {
+        callback({status: 410, token: "new-token", messages: []})
+        return {abort: jest.fn()}
+      })
+
+      longpoll.poll()
+
+      expect(mockOnerror).toHaveBeenCalledWith(410)
+      expect(mockCloseAndRetry).toHaveBeenCalledWith(3410, "session_gone", false)
+    })
   })
 
   describe("batchSend", () => {