diff --git a/addons/purchase/models/purchase.py b/addons/purchase/models/purchase.py
index a52d492895b..b7d884748b3 100644
--- a/addons/purchase/models/purchase.py
+++ b/addons/purchase/models/purchase.py
@@ -335,7 +335,7 @@ class PurchaseOrder(models.Model):
             self.filtered(lambda o: o.state == 'draft').write({'state': 'sent'})
         po_ctx = {'mail_post_autofollow': self.env.context.get('mail_post_autofollow', True)}
         if self.env.context.get('mark_rfq_as_sent'):
-            po_ctx['mail_notify_author'] = self.env.user.partner_id.id in kwargs.get('partner_ids') or []
+            po_ctx['mail_notify_author'] = self.env.user.partner_id.id in (kwargs.get('partner_ids') or [])
         return super(PurchaseOrder, self.with_context(**po_ctx)).message_post(**kwargs)
 
     def _notify_get_recipients_groups(self, msg_vals=None):
diff --git a/addons/sale/models/sale_order.py b/addons/sale/models/sale_order.py
index 274de8bd492..dfff1f3e0f8 100644
--- a/addons/sale/models/sale_order.py
+++ b/addons/sale/models/sale_order.py
@@ -1195,7 +1195,7 @@ class SaleOrder(models.Model):
             self.filtered(lambda o: o.state == 'draft').with_context(tracking_disable=True).write({'state': 'sent'})
         so_ctx = {'mail_post_autofollow': self.env.context.get('mail_post_autofollow', True)}
         if self.env.context.get('mark_so_as_sent'):
-            so_ctx['mail_notify_author'] = self.env.user.partner_id.id in kwargs.get('partner_ids') or []
+            so_ctx['mail_notify_author'] = self.env.user.partner_id.id in (kwargs.get('partner_ids') or [])
         return super(SaleOrder, self.with_context(**so_ctx)).message_post(**kwargs)
 
     def _notify_get_recipients_groups(self, msg_vals=None):