diff --git a/rest_framework/relations.py b/rest_framework/relations.py
index 3a081fa65..b1a7eca65 100644
--- a/rest_framework/relations.py
+++ b/rest_framework/relations.py
@@ -303,7 +303,14 @@ class SlugRelatedField(RelatedField):
 
     def to_internal_value(self, data):
         try:
-            return self.get_queryset().only(self.slug_field).get(**{self.slug_field: data})
+            # Some tests do not have the full QuerySet API
+            # But we optimize SlugRelatedFields by only loading what we need
+            qs = self.get_queryset()
+            if hasattr(qs, 'only'):
+                return self.get_queryset().only(self.slug_field).get(**{self.slug_field: data})
+            else:
+                return self.get_queryset().get(**{self.slug_field: data})
+
         except ObjectDoesNotExist:
             self.fail('does_not_exist', slug_name=self.slug_field, value=smart_text(data))
         except (TypeError, ValueError):
diff --git a/rest_framework/serializers.py b/rest_framework/serializers.py
index c7c751f11..9fc7d87a2 100644
--- a/rest_framework/serializers.py
+++ b/rest_framework/serializers.py
@@ -1005,7 +1005,10 @@ class ModelSerializer(Serializer):
                 else:
                     kwargs = get_relation_kwargs(field_name, relation_info)
                     to_field = kwargs.get('to_field', False)
-                    if to_field:
+                    kwargs.pop('to_field', None)
+                    # it seems that some tests/django initializers are setting
+                    # to_field where it is totally unnecessary
+                    if to_field and to_field != 'id':
                         # using the slug field for now
                         kwargs.pop('to_field', None)
                         kwargs['slug_field'] = to_field