diff --git a/rest_framework/compat.py b/rest_framework/compat.py
index dd30636f4..3125208b0 100644
--- a/rest_framework/compat.py
+++ b/rest_framework/compat.py
@@ -123,6 +123,8 @@ def get_related_model(field):
 
 
 def value_from_object(field, obj):
+    if isinstance(obj, dict):
+        return obj[field.attname]
     if django.VERSION < (1, 9):
         return field._get_val_from_obj(obj)
     field.value_from_object(obj)
diff --git a/rest_framework/fields.py b/rest_framework/fields.py
index aaf9ef14f..c77a7707a 100644
--- a/rest_framework/fields.py
+++ b/rest_framework/fields.py
@@ -1227,6 +1227,8 @@ class DurationField(Field):
         self.fail('invalid', format='[DD] [HH:[MM:]]ss[.uuuuuu]')
 
     def to_representation(self, value):
+        if isinstance(value, six.string_types):
+            return value
         return duration_string(value)
 
 
@@ -1686,4 +1688,6 @@ class ModelField(Field):
         value = value_from_object(self.model_field, obj)
         if is_protected_type(value):
             return value
+        if isinstance(obj, dict):
+            return obj[self.model_field.attname]
         return self.model_field.value_to_string(obj)