diff --git a/tests/compile-fail/concurrency/libc_pthread_join_multiple.rs b/tests/compile-fail/concurrency/libc_pthread_join_multiple.rs
index 0d99b69ed914..f8a43cfcde64 100644
--- a/tests/compile-fail/concurrency/libc_pthread_join_multiple.rs
+++ b/tests/compile-fail/concurrency/libc_pthread_join_multiple.rs
@@ -10,6 +10,7 @@
 use std::{mem, ptr};
 
 extern "C" fn thread_start(_null: *mut libc::c_void) -> *mut libc::c_void {
+    // Yield the thread several times so that other threads can join it.
     thread::yield_now();
     thread::yield_now();
     ptr::null_mut()