diff --git a/addons/sale_timesheet/models/account.py b/addons/sale_timesheet/models/account.py
index 55683a33745..bbcec43e025 100644
--- a/addons/sale_timesheet/models/account.py
+++ b/addons/sale_timesheet/models/account.py
@@ -123,7 +123,9 @@ class AccountAnalyticLine(models.Model):
                 revenue = analytic_account.currency_id.round(unit_amount * sale_price * (1-(so_line.discount/100)))
                 billable_type = 'billable_time'
             elif so_line.product_id.invoice_policy == 'order' and so_line.product_id.track_service == 'task':
-                quantity_hour = so_line.product_uom._compute_quantity(so_line.product_uom_qty, timesheet_uom)
+                quantity_hour = unit_amount
+                if so_line.product_uom.category_id == timesheet_uom.category_id:
+                    quantity_hour = so_line.product_uom._compute_quantity(so_line.product_uom_qty, timesheet_uom)
                 # compute the total revenue the SO since we are in fixed price
                 total_revenue_so = analytic_account.currency_id.round(quantity_hour * sale_price * (1-(so_line.discount/100)))
                 # compute the total revenue already existing (without the current timesheet line)