diff --git a/magmap/io/cli.py b/magmap/io/cli.py
index 99e5ca57..3fb29d37 100644
--- a/magmap/io/cli.py
+++ b/magmap/io/cli.py
@@ -81,7 +81,7 @@ def _parse_none(
 
     """
     if not libmag.is_seq(none):
-        none = tuple(none)
+        none = [none]
     if arg.lower() in none:
         return None
     return arg if fn is None else fn(arg)