diff --git a/addons/crm/models/calendar.py b/addons/crm/models/calendar.py
index 8a13f3d3a17..1d1c07154a8 100644
--- a/addons/crm/models/calendar.py
+++ b/addons/crm/models/calendar.py
@@ -7,6 +7,17 @@ from odoo import api, fields, models
 class CalendarEvent(models.Model):
     _inherit = 'calendar.event'
 
+    def _is_crm_lead(self, defaults, ctx=None):
+        """
+            This method checks if the concerned model is a CRM lead.
+            The information is not always in the defaults values,
+            this is why it is necessary to check the context too.
+        """
+        res_model = defaults.get('res_model', False) or ctx and ctx.get('default_res_model')
+        res_model_id = defaults.get('res_model_id', False) or ctx and ctx.get('default_res_model_id')
+
+        return res_model and res_model == 'crm.lead' or res_model_id and self.env['ir.model'].sudo().browse(res_model_id).model == 'crm.lead'
+
     @api.model
     def default_get(self, fields):
         if self.env.context.get('default_opportunity_id'):
@@ -17,9 +28,10 @@ class CalendarEvent(models.Model):
         defaults = super(CalendarEvent, self).default_get(fields)
 
         # sync res_model / res_id to opportunity id (aka creating meeting from lead chatter)
-        if 'opportunity_id' not in defaults and defaults.get('res_id') and (defaults.get('res_model') or defaults.get('res_model_id')):
-            if (defaults.get('res_model') and defaults['res_model'] == 'crm.lead') or (defaults.get('res_model_id') and self.env['ir.model'].sudo().browse(defaults['res_model_id']).model == 'crm.lead'):
-                defaults['opportunity_id'] = defaults['res_id']
+        ctx = self.env.context
+        if 'opportunity_id' not in defaults:
+            if self._is_crm_lead(defaults, ctx):
+                defaults['opportunity_id'] = defaults.get('res_id', False) or ctx.get('default_res_id', False)
 
         return defaults