1 files changed, 9 insertions, 0 deletions

diff --git a/src/mailman/rest/validator.py b/src/mailman/rest/validator.py
index 867991a36..d09886e36 100644
--- a/src/mailman/rest/validator.py
+++ b/src/mailman/rest/validator.py
@@ -22,6 +22,7 @@ __all__ = [
     'Validator',
     'enum_validator',
     'language_validator',
+    'list_of_strings_validator',
     'subscriber_validator',
     ]
 
@@ -66,6 +67,14 @@ def language_validator(code):
     return getUtility(ILanguageManager)[code]
 
 
+def list_of_strings_validator(values):
+    """Turn a list of things into a list of unicodes."""
+    for value in values:
+        if not isinstance(value, str):
+            raise ValueError('Expected str, got {!r}'.format(value))
+    return values
+
+
 
 class Validator:
     """A validator of parameter input."""