diff --git a/doctor/types.py b/doctor/types.py
index <HASH>..<HASH> 100644
--- a/doctor/types.py
+++ b/doctor/types.py
@@ -290,7 +290,7 @@ class Enum(SuperType, str):
     """
     native_type = str
     errors = {
-        'invalid': 'Must be a valid choice. {enum}',
+        'invalid': 'Must be one of: {enum}',
     }
     #: A list of valid values.
     enum = []  # type: typing.List[str]
diff --git a/test/test_types.py b/test/test_types.py
index <HASH>..<HASH> 100644
--- a/test/test_types.py
+++ b/test/test_types.py
@@ -277,7 +277,7 @@ class TestEnum(object):
         E('foo')
         E('bar')
         # not in choices
-        expected_msg = "Must be a valid choice. \['foo', 'bar'\]"
+        expected_msg = "Must be one of: \['foo', 'bar'\]"
         with pytest.raises(TypeSystemError, match=expected_msg):
             E('dog')
Updated error message to be more readable