diff --git a/ci/dictionary.txt b/ci/dictionary.txt
index 3a780fd7ad..a910123062 100644
--- a/ci/dictionary.txt
+++ b/ci/dictionary.txt
@@ -160,7 +160,6 @@ Filesystem
 filesystem's
 filesystems
 Firefox
-FnBox
 FnMut
 FnOnce
 formatter
diff --git a/src/ch20-03-graceful-shutdown-and-cleanup.md b/src/ch20-03-graceful-shutdown-and-cleanup.md
index f36fa026ee..3a3c14f707 100644
--- a/src/ch20-03-graceful-shutdown-and-cleanup.md
+++ b/src/ch20-03-graceful-shutdown-and-cleanup.md
@@ -450,17 +450,7 @@ pub struct ThreadPool {
     sender: mpsc::Sender<Message>,
 }
 
-trait FnBox {
-    fn call_box(self: Box<Self>);
-}
-
-impl<F: FnOnce()> FnBox for F {
-    fn call_box(self: Box<F>) {
-        (*self)()
-    }
-}
-
-type Job = Box<dyn FnBox + Send + 'static>;
+type Job = Box<dyn FnOnce + Send + 'static>;
 
 impl ThreadPool {
     /// Create a new ThreadPool.
@@ -536,7 +526,7 @@ impl Worker {
                     Message::NewJob(job) => {
                         println!("Worker {} got a job; executing.", id);
 
-                        job.call_box();
+                        (job)();
                     },
                     Message::Terminate => {
                         println!("Worker {} was told to terminate.", id);