diff --git a/trytond/tests/test_tools.py b/trytond/tests/test_tools.py
index d810a8eacd..3ea68a8481 100644
--- a/trytond/tests/test_tools.py
+++ b/trytond/tests/test_tools.py
@@ -570,6 +570,11 @@ class DomainInversionTestCase(unittest.TestCase):
         self.assertEqual(
             simplify(domain), ['OR', ['x', '=', 3], ['y', '=', 5]])
 
+        domain = ['OR', ('x', '=', 1), ['OR', ('x', '=', 2), ('x', '=', 3)]]
+        self.assertEqual(
+            simplify(domain),
+            ['OR', ('x', '=', 1), ('x', '=', 2), ('x', '=', 3)])
+
         domain = [['x', '=', 3], ['OR']]
         self.assertEqual(simplify(domain), [['x', '=', 3]])
 
diff --git a/trytond/tools/domain_inversion.py b/trytond/tools/domain_inversion.py
index 2165b645d7..5af1a6b0f6 100644
--- a/trytond/tools/domain_inversion.py
+++ b/trytond/tools/domain_inversion.py
@@ -307,9 +307,14 @@ def simplify_nested(domain):
         domain_op = bool_operator(domain)
         for branch in domain:
             simplified_branch = simplify_nested(branch)
-            if (bool_operator(branch) == domain_op
+            if (bool_operator(simplified_branch) == domain_op
                     or len(simplified_branch) == 1):
-                simplified.extend(simplified_branch)
+                if (simplified
+                        and simplified_branch
+                        and simplified_branch[0] in ['AND', 'OR']):
+                    simplified.extend(simplified_branch[1:])
+                else:
+                    simplified.extend(simplified_branch)
             else:
                 simplified.append(simplified_branch)
         return simplified