diff --git a/addons/sale_timesheet/models/sale_timesheet.py b/addons/sale_timesheet/models/sale_timesheet.py
index 6c1f1d28eb2..bcbb2b88f48 100644
--- a/addons/sale_timesheet/models/sale_timesheet.py
+++ b/addons/sale_timesheet/models/sale_timesheet.py
@@ -21,6 +21,7 @@ class ResCompany(models.Model):
 
 class HrEmployee(models.Model):
     _inherit = 'hr.employee'
+    # FIXME: this field should be in module hr_timesheet, not sale_timesheet
     timesheet_cost = fields.Float(string='Timesheet Cost', default=0.0)
 
 
@@ -43,7 +44,10 @@ class AccountAnalyticLine(models.Model):
     def _get_sale_order_line(self, vals=None):
         result = dict(vals or {})
         if self.is_timesheet:
-            sol = result.get('so_line', False) or self.so_line
+            if result.get('so_line'):
+                sol = self.env['sale.order.line'].browse([result['so_line']])
+            else:
+                sol = self.so_line
             if not sol and self.account_id:
                 sol = self.env['sale.order.line'].search([
                     ('order_id.project_id', '=', self.account_id.id),
@@ -51,27 +55,59 @@ class AccountAnalyticLine(models.Model):
                     ('product_id.track_service', '=', 'timesheet'),
                     ('product_id.type', '=', 'service')],
                     limit=1)
-            else:
-                sol = self.so_line
             if sol:
-                emp = self.env['hr.employee'].search([('user_id', '=', self.user_id.id)], limit=1)
-                if result.get('amount', False):
-                    amount = result['amount']
-                elif emp and emp.timesheet_cost:
-                    amount = -self.unit_amount * emp.timesheet_cost
-                elif self.product_id and self.product_id.standard_price:
-                    amount = -self.unit_amount * self.product_id.standard_price
-                else:
-                    amount = self.amount or 0.0
                 result.update({
-                    'product_id': sol.product_id.id,
-                    'product_uom_id': self.env.user.company_id.project_time_mode_id.id or sol.product_id.uom_id.id,
-                    'amount': amount,
                     'so_line': sol.id,
+                    'product_id': sol.product_id.id,
                 })
+                result = self._get_timesheet_cost(result)
+
         result = super(AccountAnalyticLine, self)._get_sale_order_line(vals=result)
         return result
 
+    def _get_timesheet_cost(self, vals=None):
+        result = dict(vals or {})
+        if result.get('is_timesheet') or self.is_timesheet:
+            if result.get('amount'):
+                return result
+
+            unit_amount = result.get('unit_amount', 0.0) or self.unit_amount
+            user_id = result.get('user_id', False) or self.user_id.id
+            emp = self.env['hr.employee'].search([('user_id', '=', user_id)], limit=1)
+
+            if emp and emp.timesheet_cost:
+                # Most common case: cost obtained on employee
+                result.update({
+                    'amount': -unit_amount * emp.timesheet_cost,
+                    'product_uom_id': emp.user_id.company_id.project_time_mode_id.id,
+                })
+            elif result.get('product_id'):
+                # Only useful for _get_sale_order_line since it can add a product_id.
+                product = self.env['product.product'].browse([result.get('product_id')])
+                result.update({
+                    'amount': -unit_amount * product.standard_price,
+                    'product_uom_id': product.uom_id.id,
+                })
+            elif self.product_id:
+                # Only use case where this should be useful:
+                #    - no cost on employee
+                #    - modification of the unit amount of an existing entry
+                result.update({
+                    'amount': -unit_amount * self.product_id.standard_price,
+                    'product_uom_id': self.product_id.uom_id.id,
+                })
+
+        return result
+
+    @api.multi
+    def write(self, values):
+        values = self._get_timesheet_cost(vals=values)
+        return super(AccountAnalyticLine, self).write(values)
+
+    @api.model
+    def create(self, values):
+        values = self._get_timesheet_cost(vals=values)
+        return super(AccountAnalyticLine, self).create(values)
 
 class SaleOrder(models.Model):
     _inherit = 'sale.order'