diff --git a/CHANGES.md b/CHANGES.md
index 8dc2017..a87b6b0 100644
--- a/CHANGES.md
+++ b/CHANGES.md
@@ -15,6 +15,19 @@ To be released.
 [#227]: https://github.com/spoqa/nirum/pull/227
 
 
+Version 0.3.1
+-------------
+
+Released on March 1, 2018.
+
+### Python target
+
+ -  Fixed record/union deserializers to ignore unknown fields in data payload.
+    Deserializers had raised `KeyError` before.  [[#232]]
+
+[#232]: https://github.com/spoqa/nirum/issues/232
+
+
 Version 0.3.0
 -------------
 
@@ -180,7 +193,6 @@ Released on February 18, 2018.
 [#203]: https://github.com/spoqa/nirum/pull/203
 [#204]: https://github.com/spoqa/nirum/pull/204
 [#216]: https://github.com/spoqa/nirum/issues/216
-[#222]: https://github.com/spoqa/nirum/pull/222
 [#218]: https://github.com/spoqa/nirum/issues/218
 [#222]: https://github.com/spoqa/nirum/pull/222
 [#223]: https://github.com/spoqa/nirum/pull/223
diff --git a/docs/refactoring.md b/docs/refactoring.md
index 2bec351..687263a 100644
--- a/docs/refactoring.md
+++ b/docs/refactoring.md
@@ -129,6 +129,15 @@ returns, but in program codes we become able to deal with distance using `meter`
 type rather than primitive `bigint` type.
 
 
+Removing a field
+----------------
+
+Any fields in payload that are unlisted in an interface definition are ignored
+by a deserializer.  If you are going to remove an existing field you should
+deploy the newer version to a payload consumer first, and then a payload
+provider last.
+
+
 Interchangeability of enum type and `text`
 ------------------------------------------
 
diff --git a/docs/serialization.md b/docs/serialization.md
index 9bf5f17..3652f6c 100644
--- a/docs/serialization.md
+++ b/docs/serialization.md
@@ -201,6 +201,10 @@ It's represented in JSON to:
         "uri": null
     }
 
+When a payload is deserialized, undefined fields are just ignored.
+It can be used to drop an existing field without breaking
+backward compatibility.
+
 
 Union type
 ----------
@@ -243,6 +247,9 @@ It's represented in JSON to:
         "uri": null
     }
 
+In a similar way to a recrod type, undefined fields in a payload are ignored
+by deserializer.
+
 
 Option type
 -----------
diff --git a/src/Nirum/Targets/Python.hs b/src/Nirum/Targets/Python.hs
index 0a97689..b7c382c 100644
--- a/src/Nirum/Targets/Python.hs
+++ b/src/Nirum/Targets/Python.hs
@@ -948,7 +948,11 @@ class $className(object):
             else:
                 name = attribute_name
             try:
-                args[name] = deserialize_meta(field_types[name], item)
+                field_type = field_types[name]
+            except KeyError:
+                continue
+            try:
+                args[name] = deserialize_meta(field_type, item)
             except ValueError as e:
                 errors.add('%s: %s' % (attribute_name, str(e)))
         if errors:
@@ -1097,7 +1101,11 @@ class #{className}(#{T.intercalate "," $ compileExtendClasses annotations}):
                 name = attribute_name
             tag_types = dict(cls.__nirum_tag_types__())
             try:
-                args[name] = deserialize_meta(tag_types[name], item)
+                field_type = tag_types[name]
+            except KeyError:
+                continue
+            try:
+                args[name] = deserialize_meta(field_type, item)
             except ValueError as e:
                 errors.add('%s: %s' % (attribute_name, str(e)))
         if errors:
diff --git a/test/python/primitive_test.py b/test/python/primitive_test.py
index 65aeda5..103f823 100644
--- a/test/python/primitive_test.py
+++ b/test/python/primitive_test.py
@@ -138,10 +138,18 @@ def test_record():
     point2_serialize = {'_type': 'point2', 'left': 3, 'top': 14}
     assert point2.__nirum_serialize__() == point2_serialize
     assert Point2.__nirum_deserialize__(point2_serialize) == point2
-    with raises(ValueError):
+    with raises(ValueError):  # no "_type" -- FIXME: "_type" is unnecessary
         Point2.__nirum_deserialize__({'left': 3, 'top': 14})
-    with raises(ValueError):
+    with raises(ValueError):  # no "left" and "top" fields
         Point2.__nirum_deserialize__({'_type': 'foo'})
+    p = Point2.__nirum_deserialize__({
+        # extra field does not matter; just ignored
+        '_type': 'point2',
+        'left': 3,
+        'top': 14,
+        'extra': 'it does not matter',
+    })
+    assert p == Point2(left=IntUnbox(3), top=IntUnbox(14))
     with raises(TypeError):
         Point2(left=IntUnbox(1), top='a')
     with raises(TypeError):
@@ -266,16 +274,24 @@ def test_union():
     })
     assert isinstance(name, MixedName.EastAsianName)
     with raises(ValueError) as e:
-        MixedName.__nirum_deserialize__({
+        MixedName.__nirum_deserialize__({  # invalid field types
             '_type': 'mixed_name',
             '_tag': 'east_asian_name',
-            'family_name': 404,
-            'given_name': 503,
+            'family_name': 404,  # not a text
+            'given_name': 503,  # not a text
         })
     assert str(e.value) == '''\
 family_name: '404' is not a string.
 given_name: '503' is not a string.\
-'''
+'''  # message can contain multiple errors
+    n = MixedName.__nirum_deserialize__({  # invalid field types
+        '_type': 'mixed_name',
+        '_tag': 'east_asian_name',
+        'family_name': u'John',
+        'given_name': u'Doe',
+        'extra': u'it does not matter',
+    })
+    assert n == EastAsianName(family_name=u'John', given_name=u'Doe')
 
 
 def test_union_default_tag():