diff --git a/addons/web/static/src/js/views/calendar/calendar_controller.js b/addons/web/static/src/js/views/calendar/calendar_controller.js
index 3bfd40841dd..f90f27a46da 100644
--- a/addons/web/static/src/js/views/calendar/calendar_controller.js
+++ b/addons/web/static/src/js/views/calendar/calendar_controller.js
@@ -204,7 +204,9 @@ var CalendarController = AbstractController.extend({
      * @param {OdooEvent} event
      */
     _onDropRecord: function (event) {
-        this._updateRecord(event.data);
+        this._updateRecord(_.extend({}, event.data, {
+            'drop': true,
+        }));
     },
     /**
      * @private
diff --git a/addons/web/static/src/js/views/calendar/calendar_model.js b/addons/web/static/src/js/views/calendar/calendar_model.js
index 782f31a1bd2..fa2931a6d19 100644
--- a/addons/web/static/src/js/views/calendar/calendar_model.js
+++ b/addons/web/static/src/js/views/calendar/calendar_model.js
@@ -105,7 +105,9 @@ return AbstractModel.extend({
         }
 
         if (this.mapping.date_delay) {
-            data[this.mapping.date_delay] = (end.diff(start) <= 0 ? end.endOf('day').diff(start) : end.diff(start)) / 1000 / 3600;
+            if (this.data.scale !== 'month' || (this.data.scale === 'month' && !event.drop)) {
+                data[this.mapping.date_delay] = (end.diff(start) <= 0 ? end.endOf('day').diff(start) : end.diff(start)) / 1000 / 3600;
+            }
         }
 
         return data;
diff --git a/addons/web/static/tests/views/calendar_tests.js b/addons/web/static/tests/views/calendar_tests.js
index ae8184dc7e8..e97845ea7e4 100644
--- a/addons/web/static/tests/views/calendar_tests.js
+++ b/addons/web/static/tests/views/calendar_tests.js
@@ -44,6 +44,7 @@ QUnit.module('Views', {
                     stop_date: {string: "stop date", type: "date"},
                     start: {string: "start datetime", type: "datetime"},
                     stop: {string: "stop datetime", type: "datetime"},
+                    delay: {string: "delay", type: "float"},
                     allday: {string: "allday", type: "boolean"},
                     partner_ids: {string: "attendees", type: "one2many", relation: 'partner', default: [[6, 0, [1]]]},
                     type: {string: "type", type: "integer"},
@@ -2393,6 +2394,49 @@ QUnit.module('Views', {
         calendar.destroy();
     });
 
+    QUnit.test('drag and drop on month mode with date_start and date_delay', function (assert) {
+        assert.expect(1);
+
+        var calendar = createView({
+            View: CalendarView,
+            model: 'event',
+            data: this.data,
+            arch:
+            '<calendar date_start="start" date_delay="delay" mode="month">'+
+                '<field name="name"/>'+
+                '<field name="start"/>'+
+                '<field name="delay"/>'+
+            '</calendar>',
+            archs: archs,
+            viewOptions: {
+                initialDate: initialDate,
+            },
+            mockRPC: function (route, args) {
+                if (args.method === "write") {
+                    // delay should not be written at drag and drop
+                    assert.equal(args.args[1].delay, undefined)
+                }
+                return this._super(route, args);
+            },
+        });
+
+        // Create event (on 20 december)
+        var $cell = calendar.$('.fc-day-grid .fc-row:eq(3) .fc-day:eq(2)');
+        testUtils.triggerMouseEvent($cell, "mousedown");
+        testUtils.triggerMouseEvent($cell, "mouseup");
+        var $input = $('.modal-body input:first');
+        $input.val("An event").trigger('input');
+        $('.modal button.btn:contains(Create)').trigger('click');
+
+        // Move event to another day (on 27 november)
+        testUtils.dragAndDrop(
+            calendar.$('.fc-event').first(),
+            calendar.$('.fc-day-top').first()
+        );
+
+        calendar.destroy();
+    });
+
     QUnit.test('form_view_id attribute works (for creating events)', function (assert) {
         assert.expect(1);