diff --git a/addons/mail/static/src/js/composers/basic_composer.js b/addons/mail/static/src/js/composers/basic_composer.js
index 72936152ae5..c84296d55d1 100644
--- a/addons/mail/static/src/js/composers/basic_composer.js
+++ b/addons/mail/static/src/js/composers/basic_composer.js
@@ -510,9 +510,10 @@ var BasicComposer = Widget.extend({
         clearTimeout(this._cannedTimeout);
         var self = this;
         this._preprocessMessage().then(function (message) {
-            self.trigger('post_message', message);
-            self._clearComposerOnSend();
-            self.$input.focus();
+            self.trigger('post_message', message, function() {
+                self._clearComposerOnSend();
+                self.$input.focus();
+            });
         });
     },
     /**
diff --git a/addons/mail/static/src/js/discuss.js b/addons/mail/static/src/js/discuss.js
index 4e88434f86d..8acd52d99c2 100644
--- a/addons/mail/static/src/js/discuss.js
+++ b/addons/mail/static/src/js/discuss.js
@@ -1461,8 +1461,9 @@ var Discuss = AbstractAction.extend({
     /**
      * @private
      * @param {Object} messageData
+     * @param {Function} callback
      */
-    _onPostMessage: function (messageData) {
+    _onPostMessage: function (messageData, callback) {
         var self = this;
         var options = {};
         if (this._selectedMessage) {
@@ -1483,6 +1484,7 @@ var Discuss = AbstractAction.extend({
                 } else {
                     self._threadWidget.scrollToBottom();
                 }
+                callback();
             });
     },
     /**
diff --git a/addons/mail/static/src/js/thread_windows/abstract_thread_window.js b/addons/mail/static/src/js/thread_windows/abstract_thread_window.js
index f09b78b8d3f..0af2d1080db 100644
--- a/addons/mail/static/src/js/thread_windows/abstract_thread_window.js
+++ b/addons/mail/static/src/js/thread_windows/abstract_thread_window.js
@@ -394,8 +394,9 @@ var AbstractThreadWindow = Widget.extend({
      *
      * @private
      * @param {Object} messageData
+     * @param {Function} callback
      */
-    _postMessage: function (messageData) {
+    _postMessage: function (messageData, callback) {
         var self = this;
         if (!this.hasThread()) {
             return;
@@ -403,6 +404,7 @@ var AbstractThreadWindow = Widget.extend({
         this._thread.postMessage(messageData)
             .then(function () {
                 self._threadWidget.scrollToBottom();
+                callback();
             });
     },
     /**
diff --git a/addons/mail/static/tests/discuss_tests.js b/addons/mail/static/tests/discuss_tests.js
index f25c7082648..daf34b4a5be 100644
--- a/addons/mail/static/tests/discuss_tests.js
+++ b/addons/mail/static/tests/discuss_tests.js
@@ -3,7 +3,6 @@ odoo.define('mail.discuss_test', function (require) {
 
 var mailTestUtils = require('mail.testUtils');
 
-var concurrency = require('web.concurrency');
 var testUtils = require('web.test_utils');
 
 var createDiscuss = mailTestUtils.createDiscuss;
@@ -1491,5 +1490,54 @@ QUnit.test('custom-named DM conversation', async function (assert) {
     discuss.destroy();
 });
 
+QUnit.test('input not cleared on unresolved message_post rpc', async function (assert) {
+    assert.expect(2);
+
+    // Promise to simulate late server response on message post
+    var messagePostPromise = testUtils.makeTestPromise();
+
+    this.data.initMessaging = {
+        channel_slots: {
+            channel_channel: [{
+                id: 1,
+                channel_type: "channel",
+                name: "general",
+            }],
+        },
+    };
+
+    var discuss = await createDiscuss({
+        id: 1,
+        context: {},
+        params: {},
+        data: this.data,
+        services: this.services,
+        mockRPC: function (route, args) {
+            if (args.method === 'message_post') {
+                return messagePostPromise;
+            }
+            return this._super.apply(this, arguments);
+        },
+    });
+
+    // Click on channel 'general'
+    var $general = discuss.$('.o_mail_discuss_sidebar').find('.o_mail_discuss_item[data-thread-id=1]');
+    await testUtils.dom.click($general);
+
+    // Type message
+    var $input = discuss.$('textarea.o_composer_text_field').first();
+    $input.focus();
+    $input.val('test message');
+
+    // Send message
+    await testUtils.fields.triggerKeydown($input, 'enter');
+    assert.strictEqual($input.val(), 'test message', "composer should not be cleared on send without server response");
+
+    // Simulate server response
+    messagePostPromise.resolve();
+    await testUtils.nextTick();
+    assert.strictEqual($input.val(), '', "composer should be cleared on send after server response");
+    discuss.destroy();
+});
 });
 });