diff --git a/addons/mail/static/src/js/composers/basic_composer.js b/addons/mail/static/src/js/composers/basic_composer.js
index a6cdb39e2de..8a533cd4515 100644
--- a/addons/mail/static/src/js/composers/basic_composer.js
+++ b/addons/mail/static/src/js/composers/basic_composer.js
@@ -211,7 +211,8 @@ var BasicComposer = Widget.extend({
      * displayed to the user. If none of them match, then it will fetch for more
      * partner suggestions (@see _mentionFetchPartners).
      *
-     * @param {$.Deferred<Object[]>} prefetchedPartners
+     * @param {$.Deferred<Object[]>} prefetchedPartners list of list of
+     *   prefetched partners.
      */
     mentionSetPrefetchedPartners: function (prefetchedPartners) {
         this._mentionPrefetchedPartners = prefetchedPartners;
@@ -302,21 +303,23 @@ var BasicComposer = Widget.extend({
      */
     _mentionFetchPartners: function (search) {
         var self = this;
-        return $.when(this._mentionPrefetchedPartners).then(function (partners) {
+        return $.when(this._mentionPrefetchedPartners).then(function (prefetchedPartners) {
             // filter prefetched partners with the given search string
             var suggestions = [];
             var limit = self.options.mentionFetchLimit;
             var searchRegexp = new RegExp(_.str.escapeRegExp(mailUtils.unaccent(search)), 'i');
-            if (limit > 0) {
-                var filteredPartners = _.filter(partners, function (partner) {
-                    return partner.email && searchRegexp.test(partner.email) ||
-                           partner.name && searchRegexp.test(mailUtils.unaccent(partner.name));
-                });
-                if (filteredPartners.length) {
-                    suggestions.push(filteredPartners.slice(0, limit));
-                    limit -= filteredPartners.length;
+            _.each(prefetchedPartners, function (partners) {
+                if (limit > 0) {
+                    var filteredPartners = _.filter(partners, function (partner) {
+                        return partner.email && searchRegexp.test(partner.email) ||
+                            partner.name && searchRegexp.test(mailUtils.unaccent(partner.name));
+                    });
+                    if (filteredPartners.length) {
+                        suggestions.push(filteredPartners.slice(0, limit));
+                        limit -= filteredPartners.length;
+                    }
                 }
-            }
+            });
             if (!suggestions.length && !self.options.mentionPartnersRestricted) {
                 // no result found among prefetched partners, fetch other suggestions
                 suggestions = self._mentionFetchThrottled(
diff --git a/addons/mail/static/src/js/models/threads/channel.js b/addons/mail/static/src/js/models/threads/channel.js
index 695275e799e..808e8b7fbca 100644
--- a/addons/mail/static/src/js/models/threads/channel.js
+++ b/addons/mail/static/src/js/models/threads/channel.js
@@ -179,7 +179,8 @@ var Channel = SearchableThread.extend(ThreadTypingMixin, {
     /**
      * Get listeners of a channel
      *
-     * @returns {$.Promise<Object[]>} resolved with list of channel listeners
+     * @returns {$.Promise<Array<Object[]>>} resolved with list of list of
+     *   channel listeners.
      */
     getMentionPartnerSuggestions: function () {
         var self = this;
@@ -193,7 +194,7 @@ var Channel = SearchableThread.extend(ThreadTypingMixin, {
             })
             .then(function (members) {
                 self._members = members;
-                return members;
+                return [members];
             });
         }
         return this._membersDef;
diff --git a/addons/mail/static/src/js/models/threads/livechat.js b/addons/mail/static/src/js/models/threads/livechat.js
index b7235e7bc0e..f4cb58ebad3 100644
--- a/addons/mail/static/src/js/models/threads/livechat.js
+++ b/addons/mail/static/src/js/models/threads/livechat.js
@@ -37,7 +37,8 @@ var Livechat = TwoUserChannel.extend({
      * display of a user that is typing.
      *
      * @override
-     * @returns {$.Promise<Object[]>} resolved with list of livechat members
+     * @returns {$.Promise<Array<Object[]>>} resolved with list of list of
+     *   livechat members.
      */
     getMentionPartnerSuggestions: function () {
         var self = this;
@@ -49,7 +50,7 @@ var Livechat = TwoUserChannel.extend({
                     name: self._WEBSITE_USER_NAME,
                 });
             }
-            return self._members;
+            return [self._members];
         });
     },
     /**
diff --git a/addons/mail/static/src/js/models/threads/thread.js b/addons/mail/static/src/js/models/threads/thread.js
index c9dda28dd93..b15ceb8563c 100644
--- a/addons/mail/static/src/js/models/threads/thread.js
+++ b/addons/mail/static/src/js/models/threads/thread.js
@@ -111,7 +111,7 @@ var Thread = AbstractThread.extend(ServicesMixin, {
      * By default, a thread has not listener.
      *
      * @abstract
-     * @returns {$.Promise<Object[]>}
+     * @returns {$.Promise<Array<Object[]>>}
      */
     getMentionPartnerSuggestions: function () {
         return $.when([]);
diff --git a/addons/mail/static/src/js/services/mail_manager.js b/addons/mail/static/src/js/services/mail_manager.js
index 734f12f0cf3..c21089b7095 100644
--- a/addons/mail/static/src/js/services/mail_manager.js
+++ b/addons/mail/static/src/js/services/mail_manager.js
@@ -199,7 +199,7 @@ var MailManager =  AbstractService.extend({
      * Get partners as mentions from a chatter
      * Typically all employees as partner suggestions.
      *
-     * @returns {Array<Object[]>}
+     * @returns {Array<Array<Object[]>>}
      */
     getMentionPartnerSuggestions: function () {
         return this._mentionPartnerSuggestions;
@@ -1195,8 +1195,8 @@ var MailManager =  AbstractService.extend({
      *
      * @private
      * @param {Object} result data from server on mail/init_messaging rpc
-     * @param {Object[]} result.mention_partner_suggestions list of suggestions
-     *   with all the employees
+     * @param {Array<Object[]>} result.mention_partner_suggestions list of
+     *   suggestions.
      * @param {integer} result.menu_id the menu ID of discuss app
      */
     _updateInternalStateFromServer: function (result) {
diff --git a/addons/mail/static/tests/chatter_tests.js b/addons/mail/static/tests/chatter_tests.js
index b379bc9050b..4bcce4ab352 100644
--- a/addons/mail/static/tests/chatter_tests.js
+++ b/addons/mail/static/tests/chatter_tests.js
@@ -2450,6 +2450,124 @@ QUnit.test('chatter: suggested partner auto-follow on message post', function (a
     form.destroy();
 });
 
+QUnit.test('chatter: mention prefetched partners (followers & employees)', function (assert) {
+    // Note: employees are in prefeteched partner for mentions in chatter when
+    // the module hr is installed.
+    assert.expect(10);
+
+    var followerSuggestions = [{
+        id: 1,
+        name: 'FollowerUser1',
+        email: 'follower-user1@example.com',
+    }, {
+        id: 2,
+        name: 'FollowerUser2',
+        email: 'follower-user2@example.com',
+    }];
+
+    var nonFollowerSuggestions = [{
+        id: 3,
+        name: 'NonFollowerUser1',
+        email: 'non-follower-user1@example.com',
+    }, {
+        id: 4,
+        name: 'NonFollowerUser2',
+        email: 'non-follower-user2@example.com',
+    }];
+
+    // link followers
+    this.data.partner.records[0].message_follower_ids = [10, 20];
+
+    // prefetched partners
+    this.data.initMessaging = {
+        mention_partner_suggestions: [followerSuggestions.concat(nonFollowerSuggestions)],
+    };
+
+    var form = createView({
+        View: FormView,
+        model: 'partner',
+        data: this.data,
+        services: this.services,
+        arch: '<form string="Partners">' +
+                '<sheet>' +
+                    '<field name="foo"/>' +
+                '</sheet>' +
+                '<div class="oe_chatter">' +
+                    '<field name="message_follower_ids" widget="mail_followers"/>' +
+                    '<field name="message_ids" widget="mail_thread" options="{\'display_log_button\': True}"/>' +
+                '</div>' +
+            '</form>',
+        res_id: 2,
+        mockRPC: function (route, args) {
+            if (route === '/mail/read_followers') {
+                return $.when({
+                    followers: [{
+                        id: 10,
+                        name: 'FollowerUser1',
+                        email: 'follower-user1@example.com',
+                        res_model: 'res.partner',
+                        res_id: 1,
+                    }, {
+                        id: 20,
+                        name: 'FollowerUser2',
+                        email: 'follower-user2@example.com',
+                        res_model: 'res.partner',
+                        res_id: 2,
+                    }],
+                    subtypes: [],
+                });
+            }
+            if (args.method === 'message_get_suggested_recipients') {
+                return $.when({2: []});
+            }
+            if (args.method === 'get_mention_suggestions') {
+                throw new Error('should not fetch partners for mentions');
+            }
+            return this._super(route, args);
+        },
+        session: {},
+    });
+
+    assert.strictEqual(form.$('.o_followers_count').text(), '2',
+        "should have two followers of this document");
+    assert.strictEqual(form.$('.o_followers_list > .o_partner').text().replace(/\s+/g, ''),
+        'FollowerUser1FollowerUser2',
+        "should have correct follower names");
+    assert.strictEqual(form.$('.o_composer_mention_dropdown').length, 0,
+        "should not show the mention suggestion dropdown");
+
+    form.$('.o_chatter_button_new_message').click();
+    var $input = form.$('.oe_chatter .o_composer_text_field:first()');
+    $input.val('@');
+    // the cursor position must be set for the mention manager to detect that we are mentionning
+    $input[0].selectionStart = 1;
+    $input[0].selectionEnd = 1;
+    $input.trigger('keyup');
+
+    assert.strictEqual(form.$('.o_composer_mention_dropdown').length, 1,
+        "should show the mention suggestion dropdown");
+
+    assert.strictEqual(form.$('.o_mention_proposition').length, 4,
+        "should show 4 mention suggestions");
+    assert.strictEqual(form.$('.o_mention_proposition').eq(0).text().replace(/\s+/g, ''),
+        "FollowerUser1(follower-user1@example.com)",
+        "should display correct 1st mention suggestion");
+    assert.strictEqual(form.$('.o_mention_proposition').eq(1).text().replace(/\s+/g, ''),
+        "FollowerUser2(follower-user2@example.com)",
+        "should display correct 2nd mention suggestion");
+    assert.ok(form.$('.o_mention_proposition').eq(1).next().hasClass('dropdown-divider'),
+        "should have a mention separator after last follower mention suggestion");
+    assert.strictEqual(form.$('.o_mention_proposition').eq(2).text().replace(/\s+/g, ''),
+        "NonFollowerUser1(non-follower-user1@example.com)",
+        "should display correct 3rd mention suggestion");
+    assert.strictEqual(form.$('.o_mention_proposition').eq(3).text().replace(/\s+/g, ''),
+        "NonFollowerUser2(non-follower-user2@example.com)",
+        "should display correct 4th mention suggestion");
+
+    //cleanup
+    form.destroy();
+});
+
 QUnit.module('FieldMany2ManyTagsEmail', {
     beforeEach: function () {
         this.data = {