diff -r ae376b988766 product.py
--- .a/trytond/trytond/modules/purchase/product.py	Mon Oct 20 15:02:51 2014 +0200
+++ .b/trytond/trytond/modules/purchase/product.py	Mon Nov 03 13:24:24 2014 +0100
@@ -132,11 +132,14 @@
             for product_supplier in product.product_suppliers:
                 if product_supplier.match(pattern):
                     pattern = ProductSupplierPrice.get_pattern()
-                    for price in product_supplier.prices:
-                        if price.match(quantity, uom, pattern):
-                            prices[product.id] = price.unit_price
-                            default_uom = product_supplier.uom
-                            default_currency = product_supplier.currency
+                    price = product.get_supplier_price(product_supplier,
+                        quantity, uom, pattern)
+                    if price is not None:
+                        prices[product.id] = price
+                        default_uom = product.purchase_uom
+                        default_currency = product_supplier.currency
+                    else:
+                        price = product.cost_price
                     break
             prices[product.id] = Uom.compute_price(
                 default_uom, prices[product.id], uom)
@@ -147,6 +150,13 @@
                         prices[product.id], currency, round=False)
         return prices

+    def get_supplier_price(self, product_supplier, quantity, uom, pattern):
+        res = None
+        for price in product_supplier.prices:
+            if price.match(quantity, uom, pattern):
+                res = price.unit_price
+        return res
+

 class ProductSupplier(ModelSQL, ModelView, MatchMixin):
     'Product Supplier'