diff --git a/addons/mail/static/src/js/mail.js b/addons/mail/static/src/js/mail.js
index f9ef9ef371b..29a2e076b19 100644
--- a/addons/mail/static/src/js/mail.js
+++ b/addons/mail/static/src/js/mail.js
@@ -1055,9 +1055,11 @@ openerp.mail = function (session) {
             this.is_private = datasets.is_private || false;
             this.author_id = datasets.author_id || false;
             this.thread_level = (datasets.thread_level+1) || 0;
-            this.partner_ids = datasets.partner_ids || [];
-            if (datasets.author_id && datasets.author_id[0])
-                this.partner_ids.push(datasets.author_id);
+            datasets.partner_ids = datasets.partner_ids || [];
+            if (datasets.author_id && ! _.contains(datasets.partner_ids, datasets.author_id) && datasets.author_id[0]) {
+                datasets.partner_ids.push(datasets.author_id);
+            }
+            this.partner_ids = datasets.partner_ids;
             this.messages = [];
 
             this.options.flat_mode = !!(this.options.display_indented_thread > this.thread_level ? this.options.display_indented_thread - this.thread_level : 0);
diff --git a/addons/mail/static/src/xml/mail.xml b/addons/mail/static/src/xml/mail.xml
index 5401675b0f1..4b3c31525d4 100644
--- a/addons/mail/static/src/xml/mail.xml
+++ b/addons/mail/static/src/xml/mail.xml
@@ -114,11 +114,13 @@
                 </span>
             </t>
             <t t-if="!widget.is_private and (widget.partner_ids.length or (widget.author_id and widget.author_id[0]))"> and </t>
+            <t t-set="inc" t-value="0"/>
             <t t-foreach="widget.partner_ids" t-as="partner">
                 <span t-attf-class="oe_partner_follower #{inc>=3?'oe_hidden':''}"><t t-if="inc" t-raw="', '"/>
                     <a t-if="widget.options.show_link" t-attf-href="#model=res.partner&amp;id=#{partner[0]}"><t t-raw="partner[1]"/></a>
                     <t t-if="!widget.options.show_link" t-raw="partner[1]"/>
-                </span><t t-set="inc" t-value="(inc or 0)+1"/>
+                </span>
+                <t t-set="inc" t-value="inc+1"/>
             </t>
             <t t-if="widget.partner_ids.length > 3">
                 <span class="oe_more">, <a><t t-raw="widget.partner_ids.length - 3"/> others...</a></span>