diff --git a/rest_framework/fields.py b/rest_framework/fields.py
index 41d6105ca..982aa0769 100644
--- a/rest_framework/fields.py
+++ b/rest_framework/fields.py
@@ -424,7 +424,7 @@ class Field(object):
                 if getattr(self.root, 'partial', False):
                     return empty
                 return self.default_empty_html
-            ret = dictionary[self.field_name]
+            ret = dictionary.getlist(self.field_name)
             if ret == '' and self.allow_null:
                 # If the field is blank, and null is a valid value then
                 # determine if we should use null instead.
diff --git a/rest_framework/serializers.py b/rest_framework/serializers.py
index e27610178..6e92cb5ec 100644
--- a/rest_framework/serializers.py
+++ b/rest_framework/serializers.py
@@ -11,7 +11,7 @@ python primitives.
 response content is handled by parsers and renderers.
 """
 from __future__ import unicode_literals
-
+import re
 import copy
 import inspect
 import traceback
@@ -367,10 +367,15 @@ class Serializer(BaseSerializer):
 
     @cached_property
     def _writable_fields(self):
-        return [
-            field for field in self.fields.values()
-            if (not field.read_only) or (field.default is not empty)
-        ]
+        ret = []
+        for field in self.fields.values():
+            if re.compile("\_set$").findall(field.source):
+                for field in field.child._writable_fields:
+                    ret.append(field)
+                continue
+            if (not field.read_only) or (field.default is not empty):
+                ret.append(field)
+        return ret
 
     @cached_property
     def _readable_fields(self):
@@ -454,26 +459,29 @@ class Serializer(BaseSerializer):
         ret = OrderedDict()
         errors = OrderedDict()
         fields = self._writable_fields
-
         for field in fields:
             validate_method = getattr(self, 'validate_' + field.field_name, None)
             primitive_value = field.get_value(data)
-            try:
-                validated_value = field.run_validation(primitive_value)
-                if validate_method is not None:
-                    validated_value = validate_method(validated_value)
-            except ValidationError as exc:
-                errors[field.field_name] = exc.detail
-            except DjangoValidationError as exc:
-                errors[field.field_name] = get_error_detail(exc)
-            except SkipField:
-                pass
+            validated_list = []
+            for inner_data in primitive_value:
+                try:
+                    validated_value = field.run_validation(inner_data)
+                    validated_list.append(validated_value)
+                    if validate_method is not None:
+                        validated_list.append(validate_method(validated_value))
+                except ValidationError as exc:
+                    errors[field.field_name] = exc.detail
+                except DjangoValidationError as exc:
+                    errors[field.field_name] = get_error_detail(exc)
+                except SkipField:
+                    pass
             else:
-                set_value(ret, field.source_attrs, validated_value)
-
+                if len(validated_list) > 1:
+                    set_value(ret, field.source_attrs, validated_list)
+                else:
+                    set_value(ret, field.source_attrs, validated_list[0])
         if errors:
             raise ValidationError(errors)
-
         return ret
 
     def to_representation(self, instance):