diff --git a/CHANGELOG.rst b/CHANGELOG.rst
index 70e97e60a..bfe5bf52f 100644
--- a/CHANGELOG.rst
+++ b/CHANGELOG.rst
@@ -13,6 +13,12 @@ Features:
 - Raise a `StringNotCollectionError` if ``only`` or ``exclude`` is
   passed as a string to ``fields.Nested`` (:pr:`931`).
 
+Other changes:
+
+- *Backwards-incompatible*: ``Nested`` field now defaults to ``unknown=RAISE``
+  instead of ``EXCLUDE``. This harmonizes behavior with ``Schema`` that
+  already defaults to ``RAISE`` (:issue:`908`). Thanks :user:`tuukkamustonen`.
+
 3.0.0b13 (2018-08-04)
 +++++++++++++++++++++
 
diff --git a/marshmallow/fields.py b/marshmallow/fields.py
index 16e2f33da..b5a142f40 100755
--- a/marshmallow/fields.py
+++ b/marshmallow/fields.py
@@ -12,7 +12,7 @@
 
 from marshmallow import validate, utils, class_registry
 from marshmallow.base import FieldABC, SchemaABC
-from marshmallow.utils import EXCLUDE, is_collection
+from marshmallow.utils import RAISE, is_collection
 from marshmallow.utils import missing as missing_
 from marshmallow.compat import text_type, basestring
 from marshmallow.exceptions import ValidationError, StringNotCollectionError
@@ -393,7 +393,7 @@ def __init__(self, nested, default=missing_, exclude=tuple(), only=None, **kwarg
         self.only = only
         self.exclude = exclude
         self.many = kwargs.get('many', False)
-        self.unknown = kwargs.get('unknown', EXCLUDE)
+        self.unknown = kwargs.get('unknown', RAISE)
         self.__schema = None  # Cached Schema instance
         self.__updated_fields = False
         super(Nested, self).__init__(default=default, **kwargs)
diff --git a/tests/test_decorators.py b/tests/test_decorators.py
index 59f2c360c..676f10434 100644
--- a/tests/test_decorators.py
+++ b/tests/test_decorators.py
@@ -471,7 +471,7 @@ def validate_schema(self, data, original_data, many=False):
                 raise ValidationError('Method called')
 
         class MySchema(Schema):
-            nested = fields.Nested(NestedSchema, required=True, many=True)
+            nested = fields.Nested(NestedSchema, required=True, many=True, unknown=EXCLUDE)
 
         schema = MySchema()
         errors = schema.validate({'nested': data})
diff --git a/tests/test_deserialization.py b/tests/test_deserialization.py
index 54f643b25..a0eb9c7f7 100644
--- a/tests/test_deserialization.py
+++ b/tests/test_deserialization.py
@@ -942,7 +942,7 @@ def test_exclude(self):
     def test_nested_single_deserialization_to_dict(self):
         class SimpleBlogSerializer(Schema):
             title = fields.String()
-            author = fields.Nested(SimpleUserSchema)
+            author = fields.Nested(SimpleUserSchema, unknown=EXCLUDE)
 
         blog_dict = {
             'title': 'Gimme Shelter',
diff --git a/tests/test_schema.py b/tests/test_schema.py
index f3fd9eb58..a831ebb68 100755
--- a/tests/test_schema.py
+++ b/tests/test_schema.py
@@ -10,7 +10,8 @@
 
 import pytest
 
-from marshmallow import Schema, fields, utils, validates, validates_schema, EXCLUDE
+from marshmallow import Schema, fields, utils, validates, validates_schema, \
+    EXCLUDE, INCLUDE, RAISE
 from marshmallow.exceptions import ValidationError, StringNotCollectionError
 
 from tests.base import (
@@ -1132,13 +1133,13 @@ class ChildSchema(Schema):
             str_dump_only = fields.String()
             str_load_only = fields.String()
             str_regular = fields.String()
-            grand_child = fields.Nested(GrandChildSchema)
+            grand_child = fields.Nested(GrandChildSchema, unknown=EXCLUDE)
 
         class ParentSchema(Schema):
             str_dump_only = fields.String()
             str_load_only = fields.String()
             str_regular = fields.String()
-            child = fields.Nested(ChildSchema)
+            child = fields.Nested(ChildSchema, unknown=EXCLUDE)
 
         return ParentSchema(
             dump_only=('str_dump_only', 'child.str_dump_only', 'child.grand_child.str_dump_only'),
@@ -1205,7 +1206,7 @@ class ParentSchema(Schema):
             str_dump_only = fields.String()
             str_load_only = fields.String()
             str_regular = fields.String()
-            child = fields.List(fields.Nested(ChildSchema))
+            child = fields.List(fields.Nested(ChildSchema, unknown=EXCLUDE))
 
         return ParentSchema(
             dump_only=('str_dump_only', 'child.str_dump_only'),
@@ -1972,6 +1973,33 @@ class ParentSchema(Schema):
         assert data == {'foo': {'bar': 42}, 'bar': 42}
         assert errors == {'foo': {'foo': ['Not a valid integer.']}}
 
+    @pytest.mark.parametrize('data', ({'child': {'num': 1, 'extra': 1}},))
+    @pytest.mark.parametrize(
+        'child_unknown,errors,load_raises,load_out',
+        (
+            (None, {'child': {'extra': ['Unknown field.']}}, True, None),
+            (RAISE, {'child': {'extra': ['Unknown field.']}}, True, None),
+            (INCLUDE, {}, False, {'child': {'num': 1, 'extra': 1}}),
+            (EXCLUDE, {}, False, {'child': {'num': 1}}),
+        ),
+    )
+    def test_nested_unknown_validation(self, child_unknown, errors, load_raises, load_out, data):
+
+        class ChildSchema(Schema):
+            num = fields.Int()
+
+        class ParentSchema(Schema):
+            child = fields.Nested(ChildSchema, unknown=child_unknown)
+
+        errs = ParentSchema().validate(data)
+        assert errs == errors
+        if load_raises:
+            with pytest.raises(ValidationError):
+                ParentSchema().load(data)
+        if load_out:
+            out = ParentSchema().load(data)
+            assert out == load_out
+
 
 class TestPluckSchema: