diff --git a/fastjsonschema/draft04.py b/fastjsonschema/draft04.py
index 228dc1f..b0db0be 100644
--- a/fastjsonschema/draft04.py
+++ b/fastjsonschema/draft04.py
@@ -257,7 +257,7 @@ def generate_not(self):
         else:
             with self.l('try:', optimize=False):
                 code_len = len(self._code)
-                self.generate_func_code_block(not_definition, self._variable, self._variable_name)
+                self.generate_func_code_block(not_definition, self._variable, self._variable_name, clear_variables=True)
                 if len(self._code) == code_len:
                     self.l('pass')
             self.l('except JsonSchemaValueException: pass')
diff --git a/tests/test_common.py b/tests/test_common.py
index 29a3b13..3c70dfc 100644
--- a/tests/test_common.py
+++ b/tests/test_common.py
@@ -101,6 +101,22 @@ def test_not(asserter, value, expected):
     asserter({'not': {'type': 'number'}}, value, expected)
 
 
+@pytest.mark.parametrize('value, expected', [
+    ({'a': 1}, {'a': 1}),
+    ({'b': 2}, {'b': 2}),
+    ({'a': 1, 'b': 2}, JsonSchemaValueException('data must NOT match a disallowed definition', value='{data}', name='data', definition='{definition}', rule='not')),
+])
+def test_not_with_object_and_additional_properties(asserter, value, expected):
+    # Regression test: variables created inside the not block must not leak
+    # into the outer scope (issue #208).
+    asserter({
+        'type': 'object',
+        'properties': {'a': {}, 'b': {}},
+        'additionalProperties': False,
+        'not': {'properties': {'a': {}, 'b': {}}, 'required': ['a', 'b']},
+    }, value, expected)
+
+
 exc = JsonSchemaValueException('data must NOT match a disallowed definition', value='{data}', name='data', definition='{definition}', rule='not')
 @pytest.mark.parametrize('subdefinition', [
     {'title': 'x'},