diff --git a/src/sandbox.rs b/src/sandbox.rs
index 75020b16..dda4c3f5 100644
--- a/src/sandbox.rs
+++ b/src/sandbox.rs
@@ -81,7 +81,7 @@ pub trait Sandbox {
     /// The type of __messages__ your [`Sandbox`] will produce.
     ///
     /// [`Sandbox`]: trait.Sandbox.html
-    type Message: std::fmt::Debug + Send + Clone;
+    type Message: std::fmt::Debug + Send;
 
     /// Initializes the [`Sandbox`].
     ///