diff --git a/src/gc-arena/src/arena.rs b/src/gc-arena/src/arena.rs
index 5f9e5866..381ad08e 100644
--- a/src/gc-arena/src/arena.rs
+++ b/src/gc-arena/src/arena.rs
@@ -313,7 +313,7 @@ impl<R: for<'a> Rootable<'a>> Arena<R> {
 // be 'static. If the 'gc lifetime ends up in a user type, it must either be from a type returned
 // by gc-arena (which again, knows that 'gc is really 'static), or it is in a place where it must be
 // valid that any lifetime be there since the callback is required to work for all 'gc lifetimes.
-unsafe impl<R: for<'a> Rootable<'a> + ?Sized> Send for Arena<R> where Root<'static, R>: Send {}
+unsafe impl<R: for<'a> Rootable<'a>> Send for Arena<R> where Root<'static, R>: Send {}
 
 /// Create a temporary arena without a root object and perform the given operation on it. No garbage
 /// collection will be done until the very end of the call, at which point all allocations will
diff --git a/src/gc-arena/tests/ui/arena_not_send.stderr b/src/gc-arena/tests/ui/arena_not_send.stderr
index 1b5bc6e5..e7beeb2b 100644
--- a/src/gc-arena/tests/ui/arena_not_send.stderr
+++ b/src/gc-arena/tests/ui/arena_not_send.stderr
@@ -7,7 +7,7 @@ error[E0277]: `Rc<()>` cannot be sent between threads safely
   = help: the trait `Send` is not implemented for `Rc<()>`
   = note: required for `Gc<'_, Rc<()>>` to implement `Send`
   = note: 1 redundant requirement hidden
-  = note: required for `Arena<dyn for<'gc> Rootable<'gc, for<'gc> Root = Gc<'gc, Rc<()>>>>` to implement `Send`
+  = note: required for `Arena<__DynRootable<(dyn for<'gc> Rootable<'gc, for<'gc> Root = Gc<'gc, Rc<()>>> + 'static)>>` to implement `Send`
 note: required by a bound in `assert_send`
  --> tests/ui/arena_not_send.rs:5:19
   |