diff --git a/addons/mail/static/src/js/systray/systray_messaging_menu.js b/addons/mail/static/src/js/systray/systray_messaging_menu.js
index d86e9e3913b..df35de47174 100644
--- a/addons/mail/static/src/js/systray/systray_messaging_menu.js
+++ b/addons/mail/static/src/js/systray/systray_messaging_menu.js
@@ -102,8 +102,8 @@ var MessagingMenu = Widget.extend({
         var channelUnreadCounters = _.map(channels, function (channel) {
             return channel.getUnreadCounter();
         });
-        var unreadChannelCounter = _.reduce(channelUnreadCounters, function (c1, c2) {
-            return c1 + c2;
+        var unreadChannelCounter = _.reduce(channelUnreadCounters, function (acc, c) {
+            return c > 0 ? acc + 1 : acc;
         }, 0);
         var inboxCounter = this.call('mail_service', 'getMailbox', 'inbox').getMailboxCounter();
         var mailFailureCounter = this.call('mail_service', 'getMailFailures').length;
diff --git a/addons/mail/static/tests/systray/systray_messaging_menu_tests.js b/addons/mail/static/tests/systray/systray_messaging_menu_tests.js
index f67703c4679..2f6015a0a7e 100644
--- a/addons/mail/static/tests/systray/systray_messaging_menu_tests.js
+++ b/addons/mail/static/tests/systray/systray_messaging_menu_tests.js
@@ -690,5 +690,96 @@ QUnit.test("messaging menu widget: sort dated previews before undated previews",
     messagingMenu.destroy();
 });
 
+QUnit.test('global counter with channel previews', function (assert) {
+    assert.expect(5);
+
+    var channels = [{
+        id: 1,
+        name: "channel1",
+        channel_type: "channel",
+        channel_message_ids: [1, 2],
+        message_unread_counter: 2,
+    }, {
+        id: 2,
+        name: "channel2",
+        channel_type: "channel",
+        channel_message_ids: [3],
+        message_unread_counter: 1,
+    }, {
+        id: 3,
+        name: "channel3",
+        channel_type: "channel",
+        channel_message_ids: [4],
+        message_unread_counter: 0,
+    }];
+
+    var messages = [{
+        author_id: [1, "Demo"],
+        body: "<p>message 1</p>",
+        channel_ids: [1],
+        id: 1,
+        model: 'mail.channel',
+        record_name: 'channel1',
+        res_id: 1,
+    }, {
+        author_id: [1, "Demo"],
+        body: "<p>message 2</p>",
+        channel_ids: [1],
+        id: 2,
+        model: 'mail.channel',
+        record_name: 'channel1',
+        res_id: 1,
+    }, {
+        author_id: [1, "Demo"],
+        body: "<p>message 3</p>",
+        channel_ids: [2],
+        id: 3,
+        model: 'mail.channel',
+        record_name: 'channel2',
+        res_id: 2,
+    }, {
+        author_id: [1, "Demo"],
+        body: "<p>message 4</p>",
+        channel_ids: [3],
+        id: 4,
+        model: 'mail.channel',
+        record_name: 'channel3',
+        res_id: 3,
+    }];
+
+    this.data['mail.channel'].records = channels;
+    this.data.initMessaging.channel_slots.channel_channel = channels;
+    this.data['mail.message'].records = messages;
+
+    var messagingMenu = new MessagingMenu();
+    testUtils.addMockEnvironment(messagingMenu, {
+        services: this.services,
+        data: this.data,
+        session: {
+            partner_id: 3,
+        },
+    });
+    messagingMenu.appendTo($('#qunit-fixture'));
+    assert.strictEqual(messagingMenu.$('.o_notification_counter').text(), '2',
+        "should display a counter of 2 on the messaging menu icon");
+
+    messagingMenu.$('.dropdown-toggle').click();
+
+    assert.strictEqual(messagingMenu.$('.o_mail_preview').length, 3,
+        "should display 3 previews");
+    var $previewChannel1 = messagingMenu.$('.o_mail_preview[data-preview-id=1]');
+    var $previewChannel2 = messagingMenu.$('.o_mail_preview[data-preview-id=2]');
+    var $previewChannel3 = messagingMenu.$('.o_mail_preview[data-preview-id=3]');
+
+    assert.strictEqual($previewChannel1.data('unread-counter'), 2,
+        "preview of channel 1 should have unread counter of 2");
+    assert.strictEqual($previewChannel2.data('unread-counter'), 1,
+        "preview of channel 2 should have unread counter of 1");
+    assert.strictEqual($previewChannel3.data('unread-counter'), 0,
+        "preview of channel 3 should have unread counter of 0");
+
+    messagingMenu.destroy();
+});
+
 });
 });