diff --git a/pandas_schema/validation.py b/pandas_schema/validation.py
index f3cfab3..9d7a3ba 100644
--- a/pandas_schema/validation.py
+++ b/pandas_schema/validation.py
@@ -375,7 +375,7 @@ def __init__(self, options: typing.Iterable, case_sensitive: bool = True, **kwar
 
     @property
     def default_message(self):
-        values = ','.join(str(v) for v in self.options)
+        values = ', '.join(str(v) for v in self.options)
         return 'is not in the list of legal options ({})'.format(values)
 
     def validate(self, series: pd.Series) -> pd.Series: