diff --git a/addons/sale/models/sale.py b/addons/sale/models/sale.py
index 9fca947f6f1..fddcfed99b7 100644
--- a/addons/sale/models/sale.py
+++ b/addons/sale/models/sale.py
@@ -1246,6 +1246,9 @@ class SaleOrderLine(models.Model):
         """ Compute and write the delivered quantity of current SO lines, based on their related
             analytic lines.
         """
+        # The delivered quantity of Sales Lines in 'manual' mode should not be erased
+        self = self.filtered(lambda sol: sol.product_id.service_type != 'manual')
+
         # avoid recomputation if no SO lines concerned
         if not self:
             return False