diff --git a/addons/mail/models/mail_thread.py b/addons/mail/models/mail_thread.py
index 6b23084fca7..72c5d7af029 100644
--- a/addons/mail/models/mail_thread.py
+++ b/addons/mail/models/mail_thread.py
@@ -110,7 +110,7 @@ class MailThread(models.AbstractModel):
     message_has_error_counter = fields.Integer(
         'Number of error', compute='_compute_message_has_error',
         help="Number of messages with delivery error")
-    related_attachment_count = fields.Integer('Attachment Count', compute='_compute_related_attachment_count')
+    message_attachment_count = fields.Integer('Attachment Count', compute='_compute_message_attachment_count')
     message_main_attachment_id = fields.Many2one(string="Main Attachment", comodel_name='ir.attachment')
 
     @api.one
@@ -147,12 +147,6 @@ class MailThread(models.AbstractModel):
         # using read() below is much faster than followers.mapped('res_id')
         return [('id', 'in', [res['res_id'] for res in followers.read(['res_id'])])]
 
-    @api.multi
-    def _compute_related_attachment_count(self):
-        for record in self:
-            domain = [('res_id', '=', record.id), ('res_model', '=', self._name)]
-            record.related_attachment_count = self.env['ir.attachment'].search_count(domain)
-
     @api.multi
     @api.depends('message_follower_ids')
     def _compute_is_follower(self):
@@ -244,6 +238,16 @@ class MailThread(models.AbstractModel):
     def _search_message_has_error(self, operator, operand):
         return [('message_ids.has_error', operator, operand)]
 
+    @api.multi
+    def _compute_message_attachment_count(self):
+        read_group_var = self.env['ir.attachment'].read_group([('res_model', '=', self._name)],
+                                                              fields=['res_id'],
+                                                              groupby=['res_id'])
+
+        attachment_count_dict = dict((d['res_id'], d['res_id_count']) for d in read_group_var)
+        for record in self:
+            record.message_attachment_count = attachment_count_dict.get(record.id, 0)
+
     # ------------------------------------------------------
     # CRUD overrides for automatic subscription and logging
     # ------------------------------------------------------
diff --git a/addons/mail/static/src/js/chatter.js b/addons/mail/static/src/js/chatter.js
index 0814723caf0..780cd58deec 100644
--- a/addons/mail/static/src/js/chatter.js
+++ b/addons/mail/static/src/js/chatter.js
@@ -79,7 +79,7 @@ var Chatter = Widget.extend({
     start: function () {
         this._$topbar = this.$('.o_chatter_topbar');
         this.$('.o_topbar_right_area').append(QWeb.render('mail.chatter.Attachment.Button', {
-            count: this.record.data.related_attachment_count || 0,
+            count: this.record.data.message_attachment_count || 0,
         }));
         // render and append the buttons
         this._$topbar.prepend(QWeb.render('mail.chatter.Buttons', {
@@ -270,7 +270,7 @@ var Chatter = Widget.extend({
                         if (self._reloadAfterPost(messageData)) {
                             self.trigger_up('reload');
                         } else if (messageData.attachment_ids.length) {
-                            self.trigger_up('reload', {fieldNames: ['related_attachment_count']});
+                            self.trigger_up('reload', {fieldNames: ['message_attachment_count']});
                         }
                     });
                 });
@@ -364,7 +364,7 @@ var Chatter = Widget.extend({
      * @private
      */
      _updateAttachmentCounter: function () {
-        var count = this.record.data.related_attachment_count || 0;
+        var count = this.record.data.message_attachment_count || 0;
         this.$('.o_chatter_attachment_button_count').html(' ('+ count +')');
         this.$('.o_chatter_button_attachment').toggleClass('o_hidden', !count);
      },
diff --git a/addons/mail/static/src/js/form_renderer.js b/addons/mail/static/src/js/form_renderer.js
index e01bdf18633..21477f825c9 100644
--- a/addons/mail/static/src/js/form_renderer.js
+++ b/addons/mail/static/src/js/form_renderer.js
@@ -29,7 +29,7 @@ FormRenderer.include({
      */
     confirmChange: function (state, id, fields) {
         if (this.chatter) {
-            var chatterFields = ['related_attachment_count'].concat(_.values(this.mailFields));
+            var chatterFields = ['message_attachment_count'].concat(_.values(this.mailFields));
             var updatedMailFields = _.intersection(fields, chatterFields);
             if (updatedMailFields.length) {
                 this.chatter.update(state, updatedMailFields);
diff --git a/addons/mail/static/src/js/form_view.js b/addons/mail/static/src/js/form_view.js
index 2eaed79e8c0..0e1623d0dcf 100644
--- a/addons/mail/static/src/js/form_view.js
+++ b/addons/mail/static/src/js/form_view.js
@@ -4,7 +4,7 @@ odoo.define('mail.FormView', function (require) {
 var FormView = require('web.FormView');
 
 /**
- * This file is used to add "related_attachment_count" to fieldsInfo so we can fetch its value for the
+ * This file is used to add "message_attachment_count" to fieldsInfo so we can fetch its value for the
  * chatter's attachment button without having it explicitly declared in the form view template.
  *
  */
@@ -17,7 +17,7 @@ FormView.include({
         this._super.apply(this, arguments);
 
         if ('message_ids' in this.fieldsInfo[this.viewType]) {
-            this.fieldsInfo[this.viewType].related_attachment_count = {};
+            this.fieldsInfo[this.viewType].message_attachment_count = {};
         }
     },
 });
diff --git a/addons/mail/static/tests/chatter_tests.js b/addons/mail/static/tests/chatter_tests.js
index 379b128fe89..00705b0c26e 100644
--- a/addons/mail/static/tests/chatter_tests.js
+++ b/addons/mail/static/tests/chatter_tests.js
@@ -55,14 +55,14 @@ QUnit.module('Chatter', {
                         type: 'selection',
                         selection: [['overdue', 'Overdue'], ['today', 'Today'], ['planned', 'Planned']],
                     },
-                    related_attachment_count: {
+                    message_attachment_count: {
                         string: 'Attachment count',
                         type: 'integer',
                     },
                 },
                 records: [{
                     id: 2,
-                    related_attachment_count: 3,
+                    message_attachment_count: 3,
                     display_name: "first partner",
                     foo: "HELLO",
                     message_follower_ids: [],