diff --git a/addons/mail/static/src/js/chat_manager.js b/addons/mail/static/src/js/chat_manager.js
index 78f5547e6c8..02c4ce89852 100644
--- a/addons/mail/static/src/js/chat_manager.js
+++ b/addons/mail/static/src/js/chat_manager.js
@@ -282,6 +282,22 @@ function make_message (data) {
         a.url = '/web/content/' + a.id + '?download=true';
     });
 
+    // format date to the local only once by message
+    // can not be done in preprocess, since it alter the original value
+    if (msg.tracking_value_ids && msg.tracking_value_ids.length) {
+        _.each(msg.tracking_value_ids, function(f) {
+            if (_.contains(['date', 'datetime'], f.field_type)) {
+                var format = (f.field_type === 'date') ? 'LL' : 'LLL';
+                if (f.old_value) {
+                    f.old_value = moment.utc(f.old_value).local().format(format);
+                }
+                if (f.new_value) {
+                    f.new_value = moment.utc(f.new_value).local().format(format);
+                }
+            }
+        });
+    }
+
     return msg;
 }
 
diff --git a/addons/mail/static/src/js/thread.js b/addons/mail/static/src/js/thread.js
index f0d5ae05339..ac4c50b4533 100644
--- a/addons/mail/static/src/js/thread.js
+++ b/addons/mail/static/src/js/thread.js
@@ -151,20 +151,6 @@ var Thread = Widget.extend({
             msg.hour = msg.date.format('LT');
         }
 
-        if (message.tracking_value_ids && message.tracking_value_ids.length) {
-            _.each(message.tracking_value_ids, function(f) {
-                if (_.contains(['date', 'datetime'], f.field_type)) {
-                    var format = (f.field_type === 'date') ? 'LL' : 'LLL';
-                    if (f.old_value) {
-                        f.old_value = moment.utc(f.old_value).local().format(format);
-                    }
-                    if (f.new_value) {
-                        f.new_value = moment.utc(f.new_value).local().format(format);
-                    }
-                }
-            });
-        }
-
         if (_.contains(this.expanded_msg_ids, message.id)) {
             msg.expanded = true;
         }