diff --git a/enumfields/drf/fields.py b/enumfields/drf/fields.py
index 6a7e864..bfac3c8 100644
--- a/enumfields/drf/fields.py
+++ b/enumfields/drf/fields.py
@@ -19,11 +19,17 @@ def __init__(self, enum, lenient=False, ints_as_names=False, **kwargs):
         super().__init__(**kwargs)
 
     def to_representation(self, instance):
-        assert isinstance(instance, self.enum), instance
-        if self.ints_as_names and isinstance(instance.value, int):
-            # If the enum value is an int, assume the name is more representative
-            return instance.name.lower()
-        return instance.value
+        if instance in ('', None):
+            return instance
+        try:
+            if not isinstance(instance, self.enum):
+                instance = self.enum(instance)  # Try to cast it
+            if self.ints_as_names and isinstance(instance.value, int):
+                # If the enum value is an int, assume the name is more representative
+                return instance.name.lower()
+            return instance.value
+        except ValueError:
+            raise ValueError('Invalid value [{!r}] of enum {}'.format(instance, self.enum.__name__))
 
     def to_internal_value(self, data):
         if isinstance(data, self.enum):
diff --git a/tests/enums.py b/tests/enums.py
index 5b47276..40c8f69 100644
--- a/tests/enums.py
+++ b/tests/enums.py
@@ -1,4 +1,4 @@
-from django.utils.translation import ugettext_lazy
+from django.utils.translation import gettext_lazy
 
 from enumfields import Enum, IntEnum
 
@@ -12,7 +12,7 @@ class Color(Enum):
 
     class Labels:
         RED = 'Reddish'
-        BLUE = ugettext_lazy('bluë')
+        BLUE = gettext_lazy('bluë')
 
 
 class Taste(Enum):
diff --git a/tests/test_serializers.py b/tests/test_serializers.py
index 59236f8..cb132a4 100644
--- a/tests/test_serializers.py
+++ b/tests/test_serializers.py
@@ -1,6 +1,7 @@
 import uuid
 
 import pytest
+from enumfields.drf import EnumField
 from enumfields.drf.serializers import EnumSupportSerializerMixin
 from rest_framework import serializers
 
@@ -42,6 +43,22 @@ def test_serialize(int_names):
         assert data['int_enum'] == data['int_enum_not_editable'] == IntegerEnum.B.value
 
 
+@pytest.mark.parametrize('instance, representation', [
+    ('', ''),
+    (None, None),
+    ('r', 'r'),
+    ('g', 'g'),
+    ('b', 'b'),
+])
+def test_enumfield_to_representation(instance, representation):
+    assert EnumField(Color).to_representation(instance) == representation
+
+
+def test_invalid_enumfield_to_representation():
+    with pytest.raises(ValueError, match=r"Invalid value.*"):
+        assert EnumField(Color).to_representation('INVALID_ENUM_STRING')
+
+
 @pytest.mark.django_db
 @pytest.mark.parametrize('lenient_serializer', (False, True))
 @pytest.mark.parametrize('lenient_data', (False, True))