diff --git a/rest_framework/serializers.py b/rest_framework/serializers.py
index cf491c72b..b66c83f97 100644
--- a/rest_framework/serializers.py
+++ b/rest_framework/serializers.py
@@ -808,7 +808,16 @@ class ModelSerializer(Serializer):
         raise_errors_on_nested_writes('update', self, validated_data)
 
         for attr, value in validated_data.items():
-            setattr(instance, attr, value)
+            if isinstance(value, dict):
+                instance_attr = getattr(instance, attr)
+                for _attr, _value in value.items():
+                    setattr(instance_attr, _attr, _value)
+
+                instance_attr.save()
+                setattr(instance, attr, instance_attr)
+            else:
+                setattr(instance, attr, value)
+
         instance.save()
 
         return instance