diff --git a/src/types.rs b/src/types.rs
index 40c9f01..1f1cbb5 100644
--- a/src/types.rs
+++ b/src/types.rs
@@ -47,6 +47,10 @@ pub(crate) struct AsyncPollUpvalue<'lua> {
     pub(crate) fut: LocalBoxFuture<'lua, Result<MultiValue<'lua>>>,
 }
 
+#[cfg(feature = "send")]
+pub(crate) type HookCallback = Arc<RefCell<dyn FnMut(&Lua, Debug) -> Result<()> + Send>>;
+
+#[cfg(not(feature = "send"))]
 pub(crate) type HookCallback = Arc<RefCell<dyn FnMut(&Lua, Debug) -> Result<()>>>;
 
 #[cfg(feature = "send")]