diff --git a/src/args.rs b/src/args.rs
index 10d9cb7..7ecf8ed 100644
--- a/src/args.rs
+++ b/src/args.rs
@@ -31,7 +31,7 @@ pub struct Args {
     /// This setting is passed to the tun2 crate.
     /// See [tun2::Configuration::close_fd_on_drop].
     #[cfg(unix)]
-    #[arg(long, conflicts_with = "tun")]
+    #[arg(long, value_name = "true or false", conflicts_with = "tun")]
     pub close_fd_on_drop: Option<bool>,
 
     /// Create a tun interface in a newly created unprivileged namespace