diff --git a/addons/purchase/purchase.py b/addons/purchase/purchase.py
index 70565e7e94c..076c622d3f3 100644
--- a/addons/purchase/purchase.py
+++ b/addons/purchase/purchase.py
@@ -1199,17 +1199,17 @@ class procurement_order(osv.osv):
 
     def propagate_cancel(self, cr, uid, procurement, context=None):
         if procurement.rule_id.action == 'buy' and procurement.purchase_line_id:
-            uom_obj = self.pool.get("product.uom")
             purchase_line_obj = self.pool.get('purchase.order.line')
-            uom = procurement.purchase_line_id.product_uom
-            product_qty = uom_obj._compute_qty_obj(cr, uid, procurement.product_uom, procurement.product_qty, uom, context=context)
             if procurement.purchase_line_id.state not in ('draft', 'cancel'):
                     raise osv.except_osv(_('Error!'),
                         _('Can not cancel this procurement as the related purchase order has been confirmed already.  Please cancel the purchase order first. '))
-            if float_compare(procurement.purchase_line_id.product_qty, product_qty, 0, precision_rounding=uom.rounding) > 0:
-                purchase_line_obj.write(cr, uid, [procurement.purchase_line_id.id], {'product_qty': procurement.purchase_line_id.product_qty - product_qty}, context=context)
-            else:
+
+            new_qty, new_price = self._calc_new_qty_price(cr, uid, procurement, cancel=True, context=context)
+            if new_qty != procurement.purchase_line_id.product_qty:
+                purchase_line_obj.write(cr, uid, [procurement.purchase_line_id.id], {'product_qty': new_qty, 'price_unit': new_price}, context=context)
+            if float_compare(new_qty, 0.0, precision_rounding=procurement.product_uom.rounding) != 1:
                 purchase_line_obj.action_cancel(cr, uid, [procurement.purchase_line_id.id], context=context)
+                purchase_line_obj.unlink(cr, uid, [procurement.purchase_line_id.id], context=context)
         return super(procurement_order, self).propagate_cancel(cr, uid, procurement, context=context)
 
     def _run(self, cr, uid, procurement, context=None):
@@ -1339,6 +1339,41 @@ class procurement_order(osv.osv):
             'taxes_id': [(6, 0, taxes)],
         }
 
+    def _calc_new_qty_price(self, cr, uid, procurement, po_line=None, cancel=False, context=None):
+        if not po_line:
+            po_line = procurement.purchase_line_id
+
+        uom_obj = self.pool.get('product.uom')
+        qty = uom_obj._compute_qty(cr, uid, procurement.product_uom.id, procurement.product_qty,
+            procurement.product_id.uom_po_id.id)
+        if cancel:
+            qty = -qty
+
+        # Make sure we use the minimum quantity of the partner corresponding to the PO
+        if po_line.product_id.seller_id.id == po_line.order_id.partner_id.id:
+            supplierinfo_min_qty = po_line.product_id.seller_qty
+        else:
+            supplierinfo_obj = self.pool.get('product.supplierinfo')
+            supplierinfo_ids = supplierinfo_obj.search(cr, uid, [('name', '=', po_line.order_id.partner_id.id), ('product_tmpl_id', '=', po_line.product_id.product_tmpl_id.id)])
+            supplierinfo_min_qty = supplierinfo_obj.browse(cr, uid, supplierinfo_ids).min_qty
+
+        if supplierinfo_min_qty == 0.0:
+            qty += po_line.product_qty
+        else:
+            # Recompute quantity by adding existing running procurements.
+            for proc in po_line.procurement_ids:
+                qty += uom_obj._compute_qty(cr, uid, proc.product_uom.id, proc.product_qty,
+                    proc.product_id.uom_po_id.id) if proc.state == 'running' else 0.0
+            qty = max(qty, supplierinfo_min_qty) if qty > 0.0 else 0.0
+
+        price = po_line.price_unit
+        if qty != po_line.product_qty:
+            pricelist_obj = self.pool.get('product.pricelist')
+            pricelist_id = po_line.order_id.partner_id.property_product_pricelist_purchase.id
+            price = pricelist_obj.price_get(cr, uid, [pricelist_id], procurement.product_id.id, qty, po_line.order_id.partner_id.id, {'uom': procurement.product_uom.id})[pricelist_id]
+
+        return qty, price
+
     def make_po(self, cr, uid, ids, context=None):
         """ Resolve the purchase from procurement, which may result in a new PO creation, a new PO line creation or a quantity change on existing PO line.
         Note that some operations (as the PO creation) are made as SUPERUSER because the current user may not have rights to do it (mto product launched by a sale for example)
@@ -1376,9 +1411,12 @@ class procurement_order(osv.osv):
                     available_po_line_ids = po_line_obj.search(cr, uid, [('order_id', '=', po_id), ('product_id', '=', line_vals['product_id']), ('product_uom', '=', line_vals['product_uom'])], context=context)
                     if available_po_line_ids:
                         po_line = po_line_obj.browse(cr, uid, available_po_line_ids[0], context=context)
-                        po_line_obj.write(cr, SUPERUSER_ID, po_line.id, {'product_qty': po_line.product_qty + line_vals['product_qty']}, context=context)
                         po_line_id = po_line.id
-                        sum_po_line_ids.append(procurement.id)
+                        new_qty, new_price = self._calc_new_qty_price(cr, uid, procurement, po_line=po_line, context=context)
+
+                        if new_qty > po_line.product_qty:
+                            po_line_obj.write(cr, SUPERUSER_ID, po_line.id, {'product_qty': new_qty, 'price_unit': new_price}, context=context)
+                            sum_po_line_ids.append(procurement.id)
                     else:
                         line_vals.update(order_id=po_id)
                         po_line_id = po_line_obj.create(cr, SUPERUSER_ID, line_vals, context=context)