diff --git a/src/sync.js b/src/sync.js
index f7f62344898..18cc579fb45 100644
--- a/src/sync.js
+++ b/src/sync.js
@@ -462,6 +462,16 @@ SyncApi.prototype.sync = function() {
     let savedSyncPromise = Promise.resolve();
     let savedSyncToken = null;
 
+    async function shouldAbortSync(err) {
+        if (err.errcode === "M_UNKNOWN_TOKEN") {
+            // The logout already happened, we just need to stop.
+            console.warn("Token no longer valid - assuming logout");
+            self.stop();
+            return true;
+        }
+        return false;
+    }
+
     // We need to do one-off checks before we can begin the /sync loop.
     // These are:
     //   1) We need to get push rules so we can check if events should bing as we get
@@ -479,6 +489,7 @@ SyncApi.prototype.sync = function() {
             client.pushRules = result;
         } catch (err) {
             console.error("Getting push rules failed", err);
+            if (shouldAbortSync(err)) return;
             // wait for saved sync to complete before doing anything else,
             // otherwise the sync state will end up being incorrect
             debuglog("Waiting for saved sync before retrying push rules...");
@@ -564,6 +575,7 @@ SyncApi.prototype.sync = function() {
             );
         } catch (err) {
             console.error("Getting filter failed", err);
+            if (shouldAbortSync(err)) return;
             // wait for saved sync to complete before doing anything else,
             // otherwise the sync state will end up being incorrect
             debuglog("Waiting for saved sync before retrying filter...");
@@ -877,6 +889,12 @@ SyncApi.prototype._onSyncError = function(err, syncOptions) {
     console.error("/sync error %s", err);
     console.error(err);
 
+    if (err.errcode === "M_UNKNOWN_TOKEN") {
+        console.warn("Access token no longer valid - stopping sync");
+        this.stop();
+        return;
+    }
+
     this._failedSyncCount++;
     console.log('Number of consecutive failed sync requests:', this._failedSyncCount);