diff --git a/addons/stock/stock.py b/addons/stock/stock.py
index 4510815a090..e306538d60a 100644
--- a/addons/stock/stock.py
+++ b/addons/stock/stock.py
@@ -292,6 +292,8 @@ class stock_quant(osv.osv):
         toreserve = []
         #split quants if needed
         for quant, qty in quants:
+            if qty < 0.0:
+                raise osv.except_osv(_('Error!'), _('You can not reserve negative quants. '))
             if not quant:
                 continue
             self._quant_split(cr, uid, quant, qty, context=context)