Add more Send + Sync

1 files changed, 1 insertions, 2 deletions

diff --git a/src/tree.rs b/src/tree.rs
index daac8d3..71243be 100644
--- a/src/tree.rs
+++ b/src/tree.rs
@@ -3,7 +3,6 @@
 // Licensed under the MIT license.
 // Documentation and comments licensed under CC BY-SA 4.0.
 
-#![allow(dead_code, unused_imports)] // for now
 //! Command syntax tree.
 
 use ::std::borrow::Cow;
@@ -75,7 +74,7 @@ impl<T, S, E> CommandNode<T, S, E> {
     }
 
     /// Creates a new argument node.
-    pub fn argument<A: ArgumentType<S, E> + 'static>(
+    pub fn argument<A: ArgumentType<S, E> + 'static + Send + Sync>(
         name: Cow<'static, str>,
         command: Option<Command<T, S, E>>,
         argument: A,