diff --git a/addons/purchase/purchase.py b/addons/purchase/purchase.py
index d43ed770484..5a12b17333a 100644
--- a/addons/purchase/purchase.py
+++ b/addons/purchase/purchase.py
@@ -994,7 +994,7 @@ class purchase_order_line(osv.osv):
         if not date_order:
             date_order = fields.date.context_today(self,cr,uid,context=context)
 
-        qty = qty or 1.0
+
         supplierinfo = False
         for supplier in product.seller_ids:
             if partner_id and (supplier.name.id == partner_id):
@@ -1002,13 +1002,15 @@ class purchase_order_line(osv.osv):
                 if supplierinfo.product_uom.id != uom_id:
                     res['warning'] = {'title': _('Warning!'), 'message': _('The selected supplier only sells this product by %s') % supplierinfo.product_uom.name }
                 min_qty = product_uom._compute_qty(cr, uid, supplierinfo.product_uom.id, supplierinfo.min_qty, to_uom_id=uom_id)
-                if qty < min_qty: # If the supplier quantity is greater than entered from user, set minimal.
-                    res['warning'] = {'title': _('Warning!'), 'message': _('The selected supplier has a minimal quantity set to %s %s, you should not purchase less.') % (supplierinfo.min_qty, supplierinfo.product_uom.name)}
+                if (qty or 0.0) < min_qty: # If the supplier quantity is greater than entered from user, set minimal.
+                    if qty:
+                        res['warning'] = {'title': _('Warning!'), 'message': _('The selected supplier has a minimal quantity set to %s %s, you should not purchase less.') % (supplierinfo.min_qty, supplierinfo.product_uom.name)}
                     qty = min_qty
-
         dt = self._get_date_planned(cr, uid, supplierinfo, date_order, context=context).strftime(DEFAULT_SERVER_DATETIME_FORMAT)
-
-        res['value'].update({'date_planned': date_planned or dt, 'product_qty': qty})
+        qty = qty or 1.0
+        res['value'].update({'date_planned': date_planned or dt})
+        if qty:
+            res['value'].update({'product_qty': qty})
 
         # - determine price_unit and taxes_id
         if pricelist_id:
diff --git a/addons/purchase/purchase_view.xml b/addons/purchase/purchase_view.xml
index 3124c5ebc51..15a9de84f43 100644
--- a/addons/purchase/purchase_view.xml
+++ b/addons/purchase/purchase_view.xml
@@ -205,7 +205,7 @@
                         <page string="Purchase Order">
                             <field name="order_line">
                                 <tree string="Purchase Order Lines" editable="bottom">
-                                    <field name="product_id" on_change="onchange_product_id(parent.pricelist_id,product_id,product_qty,product_uom,parent.partner_id, parent.date_order,parent.fiscal_position,date_planned,name,price_unit,context)"/>
+                                    <field name="product_id" on_change="onchange_product_id(parent.pricelist_id,product_id,0,product_uom,parent.partner_id, parent.date_order,parent.fiscal_position,date_planned,name,price_unit,context)"/>
                                     <field name="name"/>
                                     <field name="date_planned"/>
                                     <field name="company_id" groups="base.group_multi_company" widget="selection"/>
@@ -384,7 +384,7 @@
                     <sheet>
                         <group>
                             <group>
-                                <field name="product_id" on_change="onchange_product_id(parent.pricelist_id,product_id,product_qty,product_uom,parent.partner_id, parent.date_order,parent.fiscal_position,date_planned,name,price_unit,context)"/>
+                                <field name="product_id" on_change="onchange_product_id(parent.pricelist_id,product_id,0,product_uom,parent.partner_id, parent.date_order,parent.fiscal_position,date_planned,name,price_unit,context)"/>
                                 <label for="product_qty"/>
                                 <div>
                                     <field name="product_qty" on_change="onchange_product_id(parent.pricelist_id,product_id,product_qty,product_uom,parent.partner_id,parent.date_order,parent.fiscal_position,date_planned,name,price_unit,context)" class="oe_inline"/>