--- a/servo/components/style/scoped_tls.rs
+++ b/servo/components/style/scoped_tls.rs
@@ -10,16 +10,19 @@
 use rayon;
 use std::cell::{Ref, RefCell, RefMut};
 use std::ops::DerefMut;
 
 /// A scoped TLS set, that is alive during the `'scope` lifetime.
 ///
 /// We use this on Servo to construct thread-local contexts, but clear them once
 /// we're done with restyling.
+///
+/// Note that the cleanup is done on the thread that owns the scoped TLS, thus
+/// the Send bound.
 pub struct ScopedTLS<'scope, T: Send> {
     pool: &'scope rayon::ThreadPool,
     slots: Box<[RefCell<Option<T>>]>,
 }
 
 /// The scoped TLS is `Sync` because no more than one worker thread can access a
 /// given slot.
 unsafe impl<'scope, T: Send> Sync for ScopedTLS<'scope, T> {}