diff --git a/account.py b/account.py
index 5ab0da5902..4704f5b5b4 100644
--- a/account.py
+++ b/account.py
@@ -4,7 +4,8 @@ from decimal import Decimal
 import datetime
 import operator
 from itertools import izip, groupby
-from sql import Column, Literal
+
+from sql import Column, Literal, Null
 from sql.aggregate import Sum
 from sql.conditionals import Coalesce
 
@@ -70,7 +71,7 @@ class TypeTemplate(ModelSQL, ModelView):
     @staticmethod
     def order_sequence(tables):
         table, _ = tables[None]
-        return [table.sequence == None, table.sequence]
+        return [table.sequence == Null, table.sequence]
 
     @staticmethod
     def default_balance_sheet():
@@ -213,7 +214,7 @@ class Type(ModelSQL, ModelView):
     @staticmethod
     def order_sequence(tables):
         table, _ = tables[None]
-        return [table.sequence == None, table.sequence]
+        return [table.sequence == Null, table.sequence]
 
     @staticmethod
     def default_balance_sheet():
@@ -1973,12 +1974,12 @@ class ThirdPartyBalance(Report):
         cursor.execute(*line.join(move, condition=line.move == move.id
                 ).join(account, condition=line.account == account.id
                 ).select(line.party, Sum(line.debit), Sum(line.credit),
-                where=(line.party != None)
+                where=(line.party != Null)
                 & account.active
                 & account.kind.in_(('payable', 'receivable'))
                 & (account.company == data['company'])
                 & ((line.maturity_date <= Date.today())
-                    | (line.maturity_date == None))
+                    | (line.maturity_date == Null))
                 & line_query & posted_clause,
                 group_by=line.party,
                 having=(Sum(line.debit) != 0) | (Sum(line.credit) != 0)))
@@ -2128,10 +2129,10 @@ class AgedBalance(Report):
             cursor.execute(*line.join(move, condition=line.move == move.id
                     ).join(account, condition=line.account == account.id
                     ).select(line.party, Sum(line.debit) - Sum(line.credit),
-                    where=(line.party != None)
+                    where=(line.party != Null)
                     & account.active
                     & account.kind.in_(kind)
-                    & (line.reconciliation == None)
+                    & (line.reconciliation == Null)
                     & (account.company == data['company'])
                     & term_query & line_query,
                     group_by=line.party,
diff --git a/journal.py b/journal.py
index 38c1cb1a21..f02ea31be7 100644
--- a/journal.py
+++ b/journal.py
@@ -1,5 +1,7 @@
 #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 sql import Null
+
 from trytond.model import ModelView, ModelSQL, fields
 from trytond.wizard import Wizard, StateTransition
 from trytond import backend
@@ -78,7 +80,7 @@ class JournalViewColumn(ModelSQL, ModelView):
     @staticmethod
     def order_sequence(tables):
         table, _ = tables[None]
-        return [table.sequence == None, table.sequence]
+        return [table.sequence == Null, table.sequence]
 
     @staticmethod
     def default_required():
diff --git a/move.py b/move.py
index 27724b36cb..6053cd02e5 100644
--- a/move.py
+++ b/move.py
@@ -6,10 +6,7 @@ from itertools import groupby, combinations
 from operator import itemgetter
 from collections import defaultdict
 
-try:
-    from sql import Null
-except ImportError:
-    Null = None
+from sql import Null
 from sql.aggregate import Sum
 from sql.conditionals import Coalesce, Case
 
@@ -1009,7 +1006,7 @@ class Line(ModelSQL, ModelView):
             table = self.__table__()
             column = Coalesce(Sum(Coalesce(table.debit, 0)
                     - Coalesce(table.credit, 0)), 0).cast(type_name)
-            where = ((table.reconciliation == None)
+            where = ((table.reconciliation == Null)
                 & (table.party == self.party.id))
             cursor.execute(*table.select(column,
                     where=where
diff --git a/party.py b/party.py
index de9579fa15..e115cf5042 100644
--- a/party.py
+++ b/party.py
@@ -1,7 +1,8 @@
 #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 decimal import Decimal
-from sql import Literal
+
+from sql import Literal, Null
 from sql.aggregate import Sum
 from sql.conditionals import Coalesce
 
@@ -99,7 +100,7 @@ class Party:
             if name in ('receivable_today', 'payable_today'):
                 code = name[:-6]
                 today_query = ((line.maturity_date <= Date.today())
-                    | (line.maturity_date == None))
+                    | (line.maturity_date == Null))
 
             cursor.execute(*line.join(account,
                     condition=account.id == line.account
@@ -108,7 +109,7 @@ class Party:
                     where=account.active
                     & (account.kind == code)
                     & line.party.in_([p.id for p in parties])
-                    & (line.reconciliation == None)
+                    & (line.reconciliation == Null)
                     & (account.company == company_id)
                     & line_query & today_query,
                     group_by=line.party))
@@ -161,7 +162,7 @@ class Party:
         if name in ('receivable_today', 'payable_today'):
             code = name[:-6]
             today_query = ((line.maturity_date <= Date.today())
-                | (line.maturity_date == None))
+                | (line.maturity_date == Null))
 
         line_query, _ = MoveLine.query_get(line)
         Operator = fields.SQL_OPERATORS[clause[1]]
@@ -170,8 +171,8 @@ class Party:
                 ).select(line.party,
                     where=account.active
                     & (account.kind == code)
-                    & (line.party != None)
-                    & (line.reconciliation == None)
+                    & (line.party != Null)
+                    & (line.reconciliation == Null)
                     & (account.company == company_id)
                     & today_query,
                     group_by=line.party,
diff --git a/setup.py b/setup.py
index 9c769914ce..5df5a4816b 100644
--- a/setup.py
+++ b/setup.py
@@ -41,7 +41,7 @@ if minor_version % 2:
         'hg+http://hg.tryton.org/modules/%s#egg=%s-%s' % (
             name[8:], name, version))
 
-requires = ['python-dateutil', 'python-sql']
+requires = ['python-dateutil', 'python-sql >= 0.4']
 for dep in info.get('depends', []):
     if not re.match(r'(ir|res|webdav)(\W|$)', dep):
         requires.append(get_require_version('trytond_%s' % dep))
diff --git a/tax.py b/tax.py
index 6ab7434116..5386c27293 100644
--- a/tax.py
+++ b/tax.py
@@ -2,6 +2,8 @@
 #this repository contains the full copyright notices and license terms.
 import datetime
 from decimal import Decimal
+
+from sql import Null
 from sql.aggregate import Sum
 
 from trytond.model import ModelView, ModelSQL, MatchMixin, fields
@@ -419,7 +421,7 @@ class TaxTemplate(ModelSQL, ModelView):
     @staticmethod
     def order_sequence(tables):
         table, _ = tables[None]
-        return [table.sequence == None, table.sequence]
+        return [table.sequence == Null, table.sequence]
 
     @staticmethod
     def default_type():
@@ -698,7 +700,7 @@ class Tax(ModelSQL, ModelView):
     @staticmethod
     def order_sequence(tables):
         table, _ = tables[None]
-        return [table.sequence == None, table.sequence]
+        return [table.sequence == Null, table.sequence]
 
     @staticmethod
     def default_active():
@@ -1140,7 +1142,7 @@ class TaxRuleLineTemplate(ModelSQL, ModelView):
     @staticmethod
     def order_sequence(tables):
         table, _ = tables[None]
-        return [table.sequence == None, table.sequence]
+        return [table.sequence == Null, table.sequence]
 
     def _get_tax_rule_line_value(self, rule_line=None):
         '''
@@ -1254,7 +1256,7 @@ class TaxRuleLine(ModelSQL, ModelView, MatchMixin):
     @staticmethod
     def order_sequence(tables):
         table, _ = tables[None]
-        return [table.sequence == None, table.sequence]
+        return [table.sequence == Null, table.sequence]
 
     def match(self, pattern):
         if 'group' in pattern and not self.group: