diff --git a/rest_framework/fields.py b/rest_framework/fields.py
index a2b0f3bf1..b9b3ca443 100644
--- a/rest_framework/fields.py
+++ b/rest_framework/fields.py
@@ -322,16 +322,6 @@ class Field(object):
         Called when a field is added to the parent serializer instance.
         """
 
-        # In order to enforce a consistent style, we error if a redundant
-        # 'source' argument has been used. For example:
-        # my_field = serializer.CharField(source='my_field')
-        assert self.source != field_name, (
-            "It is redundant to specify `source='%s'` on field '%s' in "
-            "serializer '%s', because it is the same as the field name. "
-            "Remove the `source` keyword argument." %
-            (field_name, self.__class__.__name__, parent.__class__.__name__)
-        )
-
         self.field_name = field_name
         self.parent = parent
 
diff --git a/rest_framework/relations.py b/rest_framework/relations.py
index 744823c48..083b56bf8 100644
--- a/rest_framework/relations.py
+++ b/rest_framework/relations.py
@@ -65,14 +65,6 @@ class RelatedField(Field):
         self.queryset = kwargs.pop('queryset', self.queryset)
         self.html_cutoff = kwargs.pop('html_cutoff', self.html_cutoff)
         self.html_cutoff_text = kwargs.pop('html_cutoff_text', self.html_cutoff_text)
-        assert self.queryset is not None or kwargs.get('read_only', None), (
-            'Relational field must provide a `queryset` argument, '
-            'or set read_only=`True`.'
-        )
-        assert not (self.queryset is not None and kwargs.get('read_only', None)), (
-            'Relational fields should not provide a `queryset` argument, '
-            'when setting read_only=`True`.'
-        )
         kwargs.pop('many', None)
         kwargs.pop('allow_empty', None)
         super(RelatedField, self).__init__(**kwargs)
diff --git a/rest_framework/serializers.py b/rest_framework/serializers.py
index f7b1e1b55..3920afc24 100644
--- a/rest_framework/serializers.py
+++ b/rest_framework/serializers.py
@@ -280,11 +280,19 @@ class SerializerMetaclass(type):
         # If this class is subclassing another Serializer, add that Serializer's
         # fields.  Note that we loop over the bases in *reverse*. This is necessary
         # in order to maintain the correct order of fields.
+        all_fields = OrderedDict()
         for base in reversed(bases):
             if hasattr(base, '_declared_fields'):
-                fields = list(base._declared_fields.items()) + fields
+                for name, field in base._declared_fields.items():
+                    if name in all_fields:
+                        # Throw away old ordering, then replace with new one
+                        all_fields.pop(name)
+                    all_fields[name] = field
 
-        return OrderedDict(fields)
+        # if there are fields in both base_fields and fields, OrderedDict
+        # uses the *last* one defined. So fields needs to go last.
+        all_fields.update(OrderedDict(fields))
+        return all_fields
 
     def __new__(cls, name, bases, attrs):
         attrs['_declared_fields'] = cls._get_declared_fields(bases, attrs)
diff --git a/tests/test_serializer.py b/tests/test_serializer.py
index 741c6ab17..65dd4aca2 100644
--- a/tests/test_serializer.py
+++ b/tests/test_serializer.py
@@ -309,3 +309,85 @@ class TestCacheSerializerData:
         pickled = pickle.dumps(serializer.data)
         data = pickle.loads(pickled)
         assert data == {'field1': 'a', 'field2': 'b'}
+
+
+class TestSerializerSupportsOverriddenFields:
+    def setup(self):
+        class Base1(serializers.Serializer):
+            a_field = serializers.CharField()
+        self.Base1 = Base1
+
+        class Base2(serializers.Serializer):
+            a_field = serializers.IntegerField()
+        self.Base2 = Base2
+
+    def test_base_fields_unchanged(self):
+        """
+        Overriding a field in a subclassed serializer shouldn't change the
+        field on the superclass
+        """
+        class OverriddenFields(self.Base1):
+            a_field = serializers.FloatField()
+
+        assert isinstance(
+            self.Base1._declared_fields['a_field'],
+            serializers.CharField,
+        )
+        s = self.Base1()
+        assert isinstance(s.fields['a_field'], serializers.CharField)
+
+    def test_overridden_fields_single_base(self):
+        """
+        Subclassing a serializer and overriding a field should mean the field
+        on the subclass wins.
+        """
+        class OverriddenFieldsWithSingleBase(self.Base1):
+            a_field = serializers.FloatField()
+
+        assert isinstance(
+            OverriddenFieldsWithSingleBase._declared_fields['a_field'],
+            serializers.FloatField,
+        )
+        s = OverriddenFieldsWithSingleBase()
+        assert isinstance(s.fields['a_field'], serializers.FloatField)
+
+    def test_overridden_fields_multiple_bases(self):
+        """
+        For serializers with multiple bases, the field on the first base wins
+        (as per normal python method resolution order)
+        """
+        class OverriddenFieldsMultipleBases1(self.Base1, self.Base2):
+            # first base takes precedence; a_field should be a CharField.
+            pass
+
+        assert isinstance(
+            OverriddenFieldsMultipleBases1._declared_fields['a_field'],
+            serializers.CharField,
+        )
+        s = OverriddenFieldsMultipleBases1()
+        assert isinstance(s.fields['a_field'], serializers.CharField)
+
+        class OverriddenFieldsMultipleBases2(self.Base2, self.Base1):
+            # first base takes precedence; a_field should be a IntegerField.
+            pass
+
+        assert isinstance(
+            OverriddenFieldsMultipleBases2._declared_fields['a_field'],
+            serializers.IntegerField,
+        )
+        s = OverriddenFieldsMultipleBases2()
+        assert isinstance(s.fields['a_field'], serializers.IntegerField)
+
+    def test_overridden_fields_multiple_bases_overridden(self):
+        """
+        For serializers with multiple bases, locally defined fields still win.
+        """
+        class OverriddenFieldsMultipleBasesOverridden(self.Base1, self.Base2):
+            a_field = serializers.FloatField()
+
+        assert isinstance(
+            OverriddenFieldsMultipleBasesOverridden._declared_fields['a_field'],
+            serializers.FloatField,
+        )
+        s = OverriddenFieldsMultipleBasesOverridden()
+        assert isinstance(s.fields['a_field'], serializers.FloatField)