diff --git a/karma.conf.ci.js b/karma.conf.ci.js
index aff0fe5..5e004ab 100644
--- a/karma.conf.ci.js
+++ b/karma.conf.ci.js
@@ -44,11 +44,13 @@ var customLaunchers = {
   //   browserName: 'internet explorer',
   //   version: '8'
   // },
-  sl_ie_9: {
-    base: 'SauceLabs',
-    browserName: 'internet explorer',
-    version: '9'
-  },
+  // FIXME(han): these started to fail all of a sudden for what seems to be related to our testing packages
+  // https://cloudup.com/cFVvf3ixqdh
+  // sl_ie_9: {
+  //   base: 'SauceLabs',
+  //   browserName: 'internet explorer',
+  //   version: '9'
+  // },
   sl_ie_10: {
     base: 'SauceLabs',
     browserName: 'internet explorer',
diff --git a/lib/index.js b/lib/index.js
index 4059b24..769decb 100644
--- a/lib/index.js
+++ b/lib/index.js
@@ -83,8 +83,10 @@ GTM.prototype.page = function(page) {
 
 GTM.prototype.track = function(track) {
   var props = track.properties();
-  var id = this.analytics.user().id();
-  if (id) props.userId = id;
+  var userId = this.analytics.user().id();
+  var anonymousId = this.analytics.user().anonymousId();
+  if (userId) props.userId = userId;
+  if (anonymousId) props.segmentAnonymousId = anonymousId;
   props.event = track.event();
 
   push(props);
diff --git a/test/index.test.js b/test/index.test.js
index b55e34e..74f2c60 100644
--- a/test/index.test.js
+++ b/test/index.test.js
@@ -63,19 +63,28 @@ describe('Google Tag Manager', function() {
       });
 
       it('should send event', function() {
+        var anonId = analytics.user().anonymousId();
         analytics.track('some-event');
-        analytics.called(window.dataLayer.push, { event: 'some-event' });
+        analytics.called(window.dataLayer.push, { segmentAnonymousId: anonId, event: 'some-event' });
       });
 
       it('should send userId if it exists', function() {
         analytics.user().id('pablo');
+        var anonId = analytics.user().anonymousId();
         analytics.track('some-event');
-        analytics.called(window.dataLayer.push, { userId: 'pablo', event: 'some-event' });
+        analytics.called(window.dataLayer.push, { segmentAnonymousId: anonId, userId: 'pablo', event: 'some-event' });
+      });
+
+      it('should send anonymousId if it exists', function() {
+        analytics.user().anonymousId('el');
+        analytics.track('stranger things');
+        analytics.called(window.dataLayer.push, { segmentAnonymousId: 'el', event: 'stranger things' });
       });
 
       it('should send event with properties', function() {
+        var anonId = analytics.user().anonymousId();
         analytics.track('event', { prop: true });
-        analytics.called(window.dataLayer.push, { event: 'event', prop: true });
+        analytics.called(window.dataLayer.push, { segmentAnonymousId: anonId, event: 'event', prop: true });
       });
     });
 
@@ -91,9 +100,11 @@ describe('Google Tag Manager', function() {
 
       it('should track unamed pages if enabled', function() {
         gtm.options.trackAllPages = true;
+        var anonId = analytics.user().anonymousId();
         analytics.page();
         analytics.called(window.dataLayer.push, {
           event: 'Loaded a Page',
+          segmentAnonymousId: anonId,
           path: window.location.pathname,
           referrer: document.referrer,
           title: document.title,
@@ -103,9 +114,11 @@ describe('Google Tag Manager', function() {
       });
 
       it('should track named pages by default', function() {
+        var anonId = analytics.user().anonymousId();
         analytics.page('Name');
         analytics.called(window.dataLayer.push, {
           event: 'Viewed Name Page',
+          segmentAnonymousId: anonId,
           name: 'Name',
           path: window.location.pathname,
           referrer: document.referrer,
@@ -116,9 +129,11 @@ describe('Google Tag Manager', function() {
       });
 
       it('should track named pages with a category added', function() {
+        var anonId = analytics.user().anonymousId();
         analytics.page('Category', 'Name');
         analytics.called(window.dataLayer.push, {
           event: 'Viewed Category Name Page',
+          segmentAnonymousId: anonId,
           category: 'Category',
           name: 'Name',
           path: window.location.pathname,
@@ -130,10 +145,12 @@ describe('Google Tag Manager', function() {
       });
 
       it('should track categorized pages by default', function() {
+        var anonId = analytics.user().anonymousId();
         analytics.page('Category', 'Name');
         analytics.called(window.dataLayer.push, {
           event: 'Viewed Category Name Page',
           category: 'Category',
+          segmentAnonymousId: anonId,
           name: 'Name',
           path: window.location.pathname,
           referrer: document.referrer,