diff --git a/sao/src/pyson.js b/sao/src/pyson.js
index 8670f079aa..34bfe633cd 100644
--- a/sao/src/pyson.js
+++ b/sao/src/pyson.js
@@ -220,7 +220,7 @@
     });
 
     Sao.PYSON.Not.eval_ = function(value, context) {
-        return !value.v;
+        return !Sao.PYSON.Bool.eval_(value, context);
     };
     Sao.PYSON.Not.init_from_object = function(obj) {
         return new Sao.PYSON.Not(obj.v);
diff --git a/sao/tests/sao.js b/sao/tests/sao.js
index 9619b796bb..3f124027db 100644
--- a/sao/tests/sao.js
+++ b/sao/tests/sao.js
@@ -124,6 +124,24 @@
             'decode(Not(false))');
         QUnit.strictEqual(new Sao.PYSON.Not(true).toString(),
                 "Not(true)");
+
+        eval_ = new Sao.PYSON.Encoder().encode(new Sao.PYSON.Not({}));
+        QUnit.strictEqual(new Sao.PYSON.Decoder().decode(eval_), true,
+            "decode(Not({}))");
+
+        eval_ = new Sao.PYSON.Encoder().encode(new Sao.PYSON.Not({
+            'a': 1,
+        }));
+        QUnit.strictEqual(new Sao.PYSON.Decoder().decode(eval_), false,
+            "decode(Not({'a': 1}))");
+
+        eval_ = new Sao.PYSON.Encoder().encode(new Sao.PYSON.Not([]));
+        QUnit.strictEqual(new Sao.PYSON.Decoder().decode(eval_), true,
+            "decode(Not([]))");
+
+        eval_ = new Sao.PYSON.Encoder().encode(new Sao.PYSON.Not(['a']));
+        QUnit.strictEqual(new Sao.PYSON.Decoder().decode(eval_), false,
+            "decode(Not(['a']))");
     });
 
     QUnit.test('PYSON Bool', function() {
diff --git a/tryton/tryton/pyson.py b/tryton/tryton/pyson.py
index 0f2ed608c6..bd58b9ea1b 100644
--- a/tryton/tryton/pyson.py
+++ b/tryton/tryton/pyson.py
@@ -188,7 +188,7 @@ class Not(PYSON):
 
     @staticmethod
     def eval(dct, context):
-        return not dct['v']
+        return not Bool(dct['v']).eval(dct, context)
 
 
 class Bool(PYSON):
diff --git a/trytond/trytond/pyson.py b/trytond/trytond/pyson.py
index 85d520e693..fc7071a7c8 100644
--- a/trytond/trytond/pyson.py
+++ b/trytond/trytond/pyson.py
@@ -186,7 +186,7 @@ class Not(PYSON):
 
     @staticmethod
     def eval(dct, context):
-        return not dct['v']
+        return not Bool(dct['v']).eval(dct, context)
 
 
 class Bool(PYSON):
diff --git a/trytond/trytond/tests/test_pyson.py b/trytond/trytond/tests/test_pyson.py
index 1fb4d4e670..3fdc5407b6 100644
--- a/trytond/trytond/tests/test_pyson.py
+++ b/trytond/trytond/tests/test_pyson.py
@@ -63,6 +63,20 @@ class PYSONTestCase(unittest.TestCase):
 
         self.assertEqual(repr(pyson.Not(True)), 'Not(True)')
 
+        eval_ = pyson.PYSONEncoder().encode(pyson.Not({}))
+        self.assertTrue(pyson.PYSONDecoder().decode(eval_))
+
+        eval_ = pyson.PYSONEncoder().encode(pyson.Not({
+                    'a': 1,
+                    }))
+        self.assertFalse(pyson.PYSONDecoder().decode(eval_))
+
+        eval_ = pyson.PYSONEncoder().encode(pyson.Not([]))
+        self.assertTrue(pyson.PYSONDecoder().decode(eval_))
+
+        eval_ = pyson.PYSONEncoder().encode(pyson.Not(['a']))
+        self.assertFalse(pyson.PYSONDecoder().decode(eval_))
+
     def test_Bool(self):
         'Test pyson.Bool'
         self.assertEqual(pyson.Bool('test').pyson(), {