diff --git a/addons/stock/stock.py b/addons/stock/stock.py
index 483115bfe64..29019385a7c 100644
--- a/addons/stock/stock.py
+++ b/addons/stock/stock.py
@@ -2107,10 +2107,9 @@ class stock_inventory(osv.osv):
             context = {}
         move_obj = self.pool.get('stock.move')
         for inv in self.browse(cr, uid, ids, context=context):
-            if inv.line_ids:
-                for inventory_line in inv.line_ids:
-                    if inventory_line.product_qty < 0:
-                        raise osv.except_osv(_('Warning'),_('You cannot have a negative product quantity in an inventory line'))
+            for inventory_line in inv.line_ids:
+                if inventory_line.product_qty < 0:
+                    raise osv.except_osv(_('Warning'),_('You cannot set a negative product quantity in an inventory line'))
             if not inv.move_ids:
                 self.action_check(cr, uid, [inv.id], context=context)
             inv.refresh()
@@ -2218,27 +2217,24 @@ class stock_inventory(osv.osv):
            GROUP BY product_id, location_id, lot_id, package_id, partner_id
         ''', args)
         vals = []
-        negative_product_ids = []
         for product_line in cr.dictfetchall():
             #replace the None the dictionary by False, because falsy values are tested later on
             for key, value in product_line.items():
                 if not value:
                     product_line[key] = False
             if product_line['product_qty'] < 0:
-                summary = 'Product: '+self.pool.get('product.product').browse(cr, uid, product_line['product_id'], context=context).name+'\n'
-                summary += 'Quantity: '+str(product_line['product_qty'])+'\n'
-                summary += 'Location: '+self.pool.get('stock.location').browse(cr, uid, product_line['location_id'], context=context).complete_name+'\n'
-                summary += ('Partner: '+self.pool.get('res.partner').browse(cr, uid, product_line['partner_id'],context=context).name+'\n') if product_line['partner_id'] else ''
-                summary += ('Lot: '+self.pool.get('stock.production.lot').browse(cr, uid, product_line['prod_lot_id'], context=context).name+'\n') if product_line['prod_lot_id'] else ''
-                summary += ('Package: '+self.pool.get('stock.quant.package').browse(cr, uid, product_line['package_id'], context=context).name+'\n') if product_line['package_id'] else ''
-                raise osv.except_osv(_('Warning'),_('This product has a negative qty, please fix it before doing an inventory\n%s' % (summary)))
+                summary = _('Product: ') + product_obj.browse(cr, uid, product_line['product_id'], context=context).name + '\n'
+                summary += _('Location: ') + location_obj.browse(cr, uid, product_line['location_id'], context=context).complete_name + '\n'
+                summary += (_('Partner: ') + self.pool.get('res.partner').browse(cr, uid, product_line['partner_id'], context=context).name + '\n') if product_line['partner_id'] else ''
+                summary += (_('Lot: ') + self.pool.get('stock.production.lot').browse(cr, uid, product_line['prod_lot_id'], context=context).name + '\n') if product_line['prod_lot_id'] else ''
+                summary += (_('Package: ') + self.pool.get('stock.quant.package').browse(cr, uid, product_line['package_id'], context=context).name + '\n') if product_line['package_id'] else ''
+                raise osv.except_osv(_('Warning'),_('This inventory line has a theoretical negative quantity, please fix it before doing an inventory\n%s' % (summary)))
             product_line['inventory_id'] = inventory.id
             product_line['th_qty'] = product_line['product_qty']
             if product_line['product_id']:
                 product = product_obj.browse(cr, uid, product_line['product_id'], context=context)
                 product_line['product_uom_id'] = product.uom_id.id
             vals.append(product_line)
-
         return vals
 
 class stock_inventory_line(osv.osv):