diff --git a/purchase.odt b/purchase.odt
index 420bbd0a4b..37fd688e28 100644
Binary files a/purchase.odt and b/purchase.odt differ
diff --git a/purchase.py b/purchase.py
index c0a34feae2..5fe5b964b4 100644
--- a/purchase.py
+++ b/purchase.py
@@ -534,6 +534,7 @@ class PurchaseLine(OSV):
         ('title', 'Title'),
         ], 'Type', select=1, required=True)
     quantity = fields.Float('Quantity',
+            digits="(16, unit_digits)",
             states={
                 'invisible': "type != 'line'",
                 'required': "type == 'line'",
@@ -543,6 +544,8 @@ class PurchaseLine(OSV):
                 'required': "product",
                 'invisible': "type != 'line'",
             }, domain="[('category', '=', (product, 'product'))]")
+    unit_digits = fields.Function('get_unit_digits', type='integer',
+            string='Unit Digits', on_change_with=['unit'])
     product = fields.Many2One('product.product', 'Product',
             domain=[('purchasable', '=', True)],
             states={
@@ -639,6 +642,22 @@ class PurchaseLine(OSV):
             res[line.id] = val
         return res
 
+    def on_change_with_unit_digits(self, cursor, user, ids, vals,
+            context=None):
+        uom_obj = self.pool.get('product.uom')
+        if vals.get('unit'):
+            uom = uom_obj.browse(cursor, user, vals['unit'],
+                    context=context)
+            return uom.digits
+        return 2
+
+    def get_unit_digits(self, cursor, user, ids, name, arg, context=None):
+        res = {}
+        for line in self.browse(cursor, user, ids, context=context):
+            if line.unit:
+                res[line.id] = line.unit.digits
+        return res
+
     def on_change_product(self, cursor, user, ids, vals, context=None):
         party_obj = self.pool.get('relationship.party')
         product_obj = self.pool.get('product.product')
@@ -688,6 +707,7 @@ class PurchaseLine(OSV):
                 or vals.get('unit') not in [x.id for x in category.uoms]:
             res['unit'] = uom_obj.name_get(cursor, user, product.default_uom.id,
                     context=context)[0]
+            res['unit_digits'] = product.default_uom.digits
         return res
 
     def on_change_with_amount(self, cursor, user, ids, vals, context=None):
diff --git a/purchase.xml b/purchase.xml
index c4bbfa4056..83766be7ad 100644
--- a/purchase.xml
+++ b/purchase.xml
@@ -47,6 +47,7 @@
                                     <field name="taxes"/>
                                     <field name="amount"/>
                                     <field name="sequence" tree_invisible="1"/>
+                                    <field name="unit_digits" tree_invisible="1"/>
                                 </tree>
                             </field>
                             <group col="2" colspan="2">
@@ -568,6 +569,7 @@
                     <field name="taxes" colspan="4"/>
                     <separator name="comment" colspan="4"/>
                     <field name="comment" colspan="4"/>
+                    <field name="unit_digits" invisible="1"/>
                 </form>
                 ]]>
             </field>
@@ -588,6 +590,7 @@
                     <field name="unit_price" select="2"/>
                     <field name="taxes"/>
                     <field name="amount"/>
+                    <field name="unit_digits" tree_invisible="1"/>
                 </tree>
                 ]]>
             </field>