diff --git a/uom.py b/uom.py
index a85b7aa18e..f0943236e9 100644
--- a/uom.py
+++ b/uom.py
@@ -1,5 +1,5 @@
 #This file is part of Tryton.  The COPYRIGHT file at the top level of this repository contains the full copyright notices and license terms.
-from trytond.osv import fields, OSV
+from trytond.osv import fields, OSV, OPERATORS
 from decimal import Decimal
 
 STATES = {
@@ -188,20 +188,29 @@ class Uom(OSV):
         def process_args(args):
             i = 0
             while i < len(args):
-                if isinstance(args[i], list):
-                    process_args(args[i])
-                if isinstance(args[i], tuple) \
+                #add test for xmlrpc that doesn't handle tuple
+                if (isinstance(args[i], tuple) \
+                        or (isinstance(args[i], list) and len(args[i]) > 2 \
+                        and args[i][1] in OPERATORS)) \
                         and args[i][0] == 'category' \
                         and isinstance(args[i][2], (list, tuple)) \
                         and len(args[i][2]) == 2 \
-                        and args[i][2][1] == 'product.default_uom.category':
+                        and args[i][2][1] in ('product.default_uom.category',
+                                'uom.category'):
                     if not args[i][2][0]:
                         args[i] = ('id', '!=', '0')
                     else:
-                        product = product_obj.browse(cursor, user,
-                                args[i][2][0], context=context)
-                        category_id = product.default_uom.category.id
+                        if args[i][2][1] == 'product.default_uom.category':
+                            product = product_obj.browse(cursor, user,
+                                    args[i][2][0], context=context)
+                            category_id = product.default_uom.category.id
+                        else:
+                            uom = self.browse(cursor, user, args[i][2][0],
+                                    context=context)
+                            category_id = uom.category.id
                         args[i] = (args[i][0], args[i][1], category_id)
+                elif isinstance(args[i], list):
+                    process_args(args[i])
                 i += 1
         process_args(args)
         return super(Uom, self).search(cursor, user, args, offset=offset,