diff --git a/cli.carp b/cli.carp
index 6ddda45..4870f51 100644
--- a/cli.carp
+++ b/cli.carp
@@ -271,7 +271,7 @@ optional arguments.")
                   (Option.long arg) (Option.short arg) (Option.description arg)))
           (when @(Option.required? arg) (IO.print " REQUIRED"))
           (when (Maybe.just? (Option.default arg))
-            (IO.print &(fmt " (default: %s)" &(Maybe.unsafe-from @(Option.default arg)))))
+            (IO.print &(fmt " (default: %s)" &(str &(Maybe.unsafe-from @(Option.default arg))))))
           (match @(Option.options arg)
             (Maybe.Just o)
               (IO.print &(fmt " (options: %s)" &(join ", " &(Array.copy-map &str &o))))