diff --git a/addons/product/product.py b/addons/product/product.py
index 7a36507aa79..ff0a6a770d7 100644
--- a/addons/product/product.py
+++ b/addons/product/product.py
@@ -132,10 +132,10 @@ class product_uom(osv.osv):
         'name': fields.char('Unit of Measure', size=64, required=True, translate=True),
         'category_id': fields.many2one('product.uom.categ', 'Category', required=True, ondelete='cascade',
             help="Conversion between Units of Measure can only occur if they belong to the same category. The conversion will be made based on the ratios."),
-        'factor': fields.float('Ratio', required=True,digits=(12, 12),
+        'factor': fields.float('Ratio', required=True, digits=0, # force NUMERIC with unlimited precision
             help='How much bigger or smaller this unit is compared to the reference Unit of Measure for this category:\n'\
                     '1 * (reference unit) = ratio * (this unit)'),
-        'factor_inv': fields.function(_factor_inv, digits=(12,12),
+        'factor_inv': fields.function(_factor_inv, digits=0, # force NUMERIC with unlimited precision
             fnct_inv=_factor_inv_write,
             string='Ratio',
             help='How many times this Unit of Measure is bigger than the reference Unit of Measure in this category:\n'\
diff --git a/addons/product/product_view.xml b/addons/product/product_view.xml
index 26bc294e436..7b4539e7dd3 100644
--- a/addons/product/product_view.xml
+++ b/addons/product/product_view.xml
@@ -421,8 +421,8 @@
                             <field name="uom_type" on_change="onchange_type(uom_type)"/>
                             <label for="factor"/>
                             <div>
-                                <field name="factor" attrs="{'invisible':[('uom_type','!=','smaller')]}"/>
-                                <field name="factor_inv" attrs="{'invisible':[('uom_type','!=','bigger')]}"/>
+                                <field name="factor" digits="[42,5]" attrs="{'invisible':[('uom_type','!=','smaller')]}"/>
+                                <field name="factor_inv" digits="[42,5]" attrs="{'invisible':[('uom_type','!=','bigger')]}"/>
                                 <p attrs="{'invisible':[('uom_type','!=','smaller')]}" class="oe_grey">
                                     e.g: 1 * (reference unit) = ratio * (this unit)
                                 </p>
diff --git a/openerp/osv/orm.py b/openerp/osv/orm.py
index f934235d99d..dc949db16ad 100644
--- a/openerp/osv/orm.py
+++ b/openerp/osv/orm.py
@@ -592,7 +592,12 @@ def get_pg_type(f, type_override=None):
     if field_type in FIELDS_TO_PGTYPES:
         pg_type =  (FIELDS_TO_PGTYPES[field_type], FIELDS_TO_PGTYPES[field_type])
     elif issubclass(field_type, fields.float):
-        if f.digits:
+        # Explicit support for "falsy" digits (0, False) to indicate a
+        # NUMERIC field with no fixed precision. The values will be saved
+        # in the database with all significant digits.
+        # FLOAT8 type is still the default when there is no precision because
+        # it is faster for most operations (sums, etc.)
+        if f.digits is not None:
             pg_type = ('numeric', 'NUMERIC')
         else:
             pg_type = ('float8', 'DOUBLE PRECISION')