diff --git a/docs/api-guide/serializers.md b/docs/api-guide/serializers.md
index 7ee060af4..c4d6501a2 100644
--- a/docs/api-guide/serializers.md
+++ b/docs/api-guide/serializers.md
@@ -105,7 +105,9 @@ When deserializing data, we can either create a new instance, or update an exist
     serializer = CommentSerializer(data=data)           # Create new instance
     serializer = CommentSerializer(comment, data=data)  # Update `comment`
 
-By default, serializers must be passed values for all required fields or they will throw validation errors.  You can use the `partial` argument in order to allow partial updates.
+When creating a new instance, serializers must be passed values for all required fields or they will throw validation errors.
+
+When updating an existing instance, serializers must be passed values for every field that does not have a default specified, or they will throw validation errors.  Omitted fields will be reset to their default values.  You can use the `partial` argument in order to allow partial updates, in which case omitted fields will not be changed.
 
     serializer = CommentSerializer(comment, data={'content': u'foo bar'}, partial=True)  # Update `comment` with partial data
 
diff --git a/rest_framework/fields.py b/rest_framework/fields.py
index 68b956822..953ec2cad 100644
--- a/rest_framework/fields.py
+++ b/rest_framework/fields.py
@@ -356,7 +356,8 @@ class WritableField(Field):
                 # Note: partial updates shouldn't set defaults
                 native = self.get_default_value()
             else:
-                if self.required:
+                incomplete_update = self.root.object is not None and not self.partial
+                if self.required or incomplete_update:
                     raise ValidationError(self.error_messages['required'])
                 return
 
diff --git a/rest_framework/tests/models.py b/rest_framework/tests/models.py
index bf9883123..615b43b04 100644
--- a/rest_framework/tests/models.py
+++ b/rest_framework/tests/models.py
@@ -43,8 +43,10 @@ class SlugBasedModel(RESTFrameworkModel):
 
 
 class DefaultValueModel(RESTFrameworkModel):
+    required_field = models.CharField(max_length=100)
     text = models.CharField(default='foobar', max_length=100)
     extra = models.CharField(blank=True, null=True, max_length=100)
+    extra_not_nullable = models.CharField(blank=True, max_length=100)
 
 
 class CallableDefaultValueModel(RESTFrameworkModel):
diff --git a/rest_framework/tests/test_serializer.py b/rest_framework/tests/test_serializer.py
index 198c269f0..c02e03988 100644
--- a/rest_framework/tests/test_serializer.py
+++ b/rest_framework/tests/test_serializer.py
@@ -867,37 +867,110 @@ class DefaultValueTests(TestCase):
         self.objects = DefaultValueModel.objects
 
     def test_create_using_default(self):
-        data = {}
+        data = {'required_field': 'required_field_value'}
         serializer = self.serializer_class(data=data)
         self.assertEqual(serializer.is_valid(), True)
         instance = serializer.save()
         self.assertEqual(len(self.objects.all()), 1)
         self.assertEqual(instance.pk, 1)
         self.assertEqual(instance.text, 'foobar')
+        self.assertEqual(instance.required_field, 'required_field_value')
+        self.assertEqual(instance.extra, None)
+        self.assertEqual(instance.extra_not_nullable, '')
 
     def test_create_overriding_default(self):
-        data = {'text': 'overridden'}
+        data = {'required_field': 'required_field_value', 'text': 'overridden'}
         serializer = self.serializer_class(data=data)
         self.assertEqual(serializer.is_valid(), True)
         instance = serializer.save()
         self.assertEqual(len(self.objects.all()), 1)
         self.assertEqual(instance.pk, 1)
         self.assertEqual(instance.text, 'overridden')
+        self.assertEqual(instance.required_field, 'required_field_value')
+        self.assertEqual(instance.extra, None)
+        self.assertEqual(instance.extra_not_nullable, '')
 
     def test_partial_update_default(self):
-        """ Regression test for issue #532 """
-        data = {'text': 'overridden'}
+        """
+        Regression test for issue #532. Ensure a partial update does not modify omitted
+        fields to their default values.
+        """
+        data = {
+            'required_field': 'required_field_value',
+            'text': 'overridden',
+            'extra': 'extra_value',
+            'extra_not_nullable': 'extra_not_nullable_value',
+        }
         serializer = self.serializer_class(data=data, partial=True)
         self.assertEqual(serializer.is_valid(), True)
         instance = serializer.save()
+        self.assertEqual(instance.required_field, 'required_field_value')
+        self.assertEqual(instance.text, 'overridden')
+        self.assertEqual(instance.extra, 'extra_value')
+        self.assertEqual(instance.extra_not_nullable, 'extra_not_nullable_value')
 
-        data = {'extra': 'extra_value'}
+        data = {'extra': 'extra_updated'}
         serializer = self.serializer_class(instance=instance, data=data, partial=True)
         self.assertEqual(serializer.is_valid(), True)
         instance = serializer.save()
-
-        self.assertEqual(instance.extra, 'extra_value')
+        self.assertEqual(instance.extra, 'extra_updated')
         self.assertEqual(instance.text, 'overridden')
+        self.assertEqual(instance.required_field, 'required_field_value')
+        self.assertEqual(instance.extra_not_nullable, 'extra_not_nullable_value')
+
+    def test_non_partial_update_default(self):
+        """
+        Omitted values in a full update should be reset.
+        """
+        data = {
+            'required_field': 'required_field_value',
+            'text': 'overridden',
+            'extra': 'extra_value',
+            'extra_not_nullable': 'extra_not_nullable_value',
+        }
+        serializer = self.serializer_class(data=data)
+        self.assertTrue(serializer.is_valid())
+        instance = serializer.save()
+        self.assertEqual(instance.required_field, 'required_field_value')
+        self.assertEqual(instance.text, 'overridden')
+        self.assertEqual(instance.extra, 'extra_value')
+        self.assertEqual(instance.extra_not_nullable, 'extra_not_nullable_value')
+
+        # Omitting a required field is not valid.
+        data = {'text': 'text_updated'}
+        serializer = self.serializer_class(instance=instance, data=data)
+        self.assertFalse(serializer.is_valid())
+
+        # Omitting an optional field with no default value is not valid
+        data = {
+            'text': 'text_updated',
+            'required_field': 'required_field_updated',
+            'extra': 'extra_updated',
+        }
+        serializer = self.serializer_class(instance=instance, data=data)
+        self.assertFalse(serializer.is_valid())
+
+        data = {
+            'text': 'text_updated',
+            'required_field': 'required_field_updated',
+            'extra_not_nullable': 'extra_not_nullable_updated',
+        }
+        serializer = self.serializer_class(instance=instance, data=data)
+        self.assertFalse(serializer.is_valid())
+
+        # A field with a default value should be reset to default when omitted
+        data = {
+            'required_field': 'required_field_updated',
+            'extra': 'extra_updated',
+            'extra_not_nullable': 'extra_not_nullable_updated',
+        }
+        serializer = self.serializer_class(instance=instance, data=data)
+        self.assertTrue(serializer.is_valid())
+        instance = serializer.save()
+        self.assertEqual(instance.text, 'foobar')
+        self.assertEqual(instance.required_field, 'required_field_updated')
+        self.assertEqual(instance.extra, 'extra_updated')
+        self.assertEqual(instance.extra_not_nullable, 'extra_not_nullable_updated')
 
 
 class WritableFieldDefaultValueTests(TestCase):