diff --git a/.bumpversion.cfg b/.bumpversion.cfg
index <HASH>..<HASH> 100644
--- a/.bumpversion.cfg
+++ b/.bumpversion.cfg
@@ -1,5 +1,5 @@
 [bumpversion]
-current_version = 1.13.1
+current_version = 1.13.2
 commit = False
 tag = False
 
diff --git a/microcosm_flask/fields/enum_field.py b/microcosm_flask/fields/enum_field.py
index <HASH>..<HASH> 100644
--- a/microcosm_flask/fields/enum_field.py
+++ b/microcosm_flask/fields/enum_field.py
@@ -4,6 +4,8 @@ Enum-valued field.
 Supports both by name (preferred) and by value (discouraged) encoding.
 
 """
+from enum import Enum
+
 from marshmallow.fields import Field
 
 
@@ -28,7 +30,7 @@ class EnumField(Field):
     def _serialize(self, value, attr, obj):
         if value is None:
             return value
-        elif isinstance(value, str):
+        elif isinstance(value, str) and not isinstance(value, Enum):
             return value
         elif self.by_value:
             return value.value
diff --git a/setup.py b/setup.py
index <HASH>..<HASH> 100755
--- a/setup.py
+++ b/setup.py
@@ -2,7 +2,7 @@
 from setuptools import find_packages, setup
 
 project = "microcosm-flask"
-version = "1.13.1"
+version = "1.13.2"
 
 setup(
     name=project,
Handle enums that are both string and enum.