diff --git a/src/tools/miri/src/concurrency/thread.rs b/src/tools/miri/src/concurrency/thread.rs
index 3c5a6786bd1..5e6fcbde69a 100644
--- a/src/tools/miri/src/concurrency/thread.rs
+++ b/src/tools/miri/src/concurrency/thread.rs
@@ -32,10 +32,12 @@ pub enum SchedulingAction {
 
 /// Timeout callbacks can be created by synchronization primitives to tell the
 /// scheduler that they should be called once some period of time passes.
-pub trait TimeoutCallback<'mir, 'tcx>: VisitMachineValues + 'tcx {
+pub trait MachineCallback<'mir, 'tcx>: VisitMachineValues {
     fn call(&self, ecx: &mut InterpCx<'mir, 'tcx, MiriMachine<'mir, 'tcx>>) -> InterpResult<'tcx>;
 }
 
+type TimeoutCallback<'mir, 'tcx> = Box<dyn MachineCallback<'mir, 'tcx> + 'tcx>;
+
 /// A thread identifier.
 #[derive(Clone, Copy, Debug, PartialOrd, Ord, PartialEq, Eq, Hash)]
 pub struct ThreadId(u32);
@@ -252,7 +254,7 @@ struct TimeoutCallbackInfo<'mir, 'tcx> {
     /// The callback should be called no earlier than this time.
     call_time: Time,
     /// The called function.
-    callback: Box<dyn TimeoutCallback<'mir, 'tcx>>,
+    callback: TimeoutCallback<'mir, 'tcx>,
 }
 
 impl<'mir, 'tcx> std::fmt::Debug for TimeoutCallbackInfo<'mir, 'tcx> {
@@ -303,10 +305,10 @@ impl VisitMachineValues for ThreadManager<'_, '_> {
         let ThreadManager {
             threads,
             thread_local_alloc_ids,
+            timeout_callbacks,
             active_thread: _,
             yield_active_thread: _,
             sync: _,
-            timeout_callbacks: _,
         } = self;
 
         for thread in threads {
@@ -315,8 +317,9 @@ impl VisitMachineValues for ThreadManager<'_, '_> {
         for ptr in thread_local_alloc_ids.borrow().values().copied() {
             visit.visit(ptr);
         }
-        // FIXME: Do we need to do something for TimeoutCallback? That's a Box<dyn>, not sure what
-        // to do.
+        for callback in timeout_callbacks.values() {
+            callback.callback.visit_machine_values(visit);
+        }
     }
 }
 
@@ -542,7 +545,7 @@ impl<'mir, 'tcx: 'mir> ThreadManager<'mir, 'tcx> {
         &mut self,
         thread: ThreadId,
         call_time: Time,
-        callback: Box<dyn TimeoutCallback<'mir, 'tcx>>,
+        callback: TimeoutCallback<'mir, 'tcx>,
     ) {
         self.timeout_callbacks
             .try_insert(thread, TimeoutCallbackInfo { call_time, callback })
@@ -558,7 +561,7 @@ impl<'mir, 'tcx: 'mir> ThreadManager<'mir, 'tcx> {
     fn get_ready_callback(
         &mut self,
         clock: &Clock,
-    ) -> Option<(ThreadId, Box<dyn TimeoutCallback<'mir, 'tcx>>)> {
+    ) -> Option<(ThreadId, TimeoutCallback<'mir, 'tcx>)> {
         // We iterate over all threads in the order of their indices because
         // this allows us to have a deterministic scheduler.
         for thread in self.threads.indices() {
@@ -931,7 +934,7 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriInterpCxExt<'mir, 'tcx> {
         &mut self,
         thread: ThreadId,
         call_time: Time,
-        callback: Box<dyn TimeoutCallback<'mir, 'tcx>>,
+        callback: TimeoutCallback<'mir, 'tcx>,
     ) {
         let this = self.eval_context_mut();
         if !this.machine.communicate() && matches!(call_time, Time::RealTime(..)) {
diff --git a/src/tools/miri/src/shims/time.rs b/src/tools/miri/src/shims/time.rs
index 43792024e2c..05eff3dfd59 100644
--- a/src/tools/miri/src/shims/time.rs
+++ b/src/tools/miri/src/shims/time.rs
@@ -1,6 +1,6 @@
 use std::time::{Duration, SystemTime};
 
-use crate::concurrency::thread::TimeoutCallback;
+use crate::concurrency::thread::MachineCallback;
 use crate::*;
 
 /// Returns the time elapsed between the provided time and the unix epoch as a `Duration`.
@@ -257,7 +257,7 @@ impl VisitMachineValues for Callback {
     fn visit_machine_values(&self, _visit: &mut ProvenanceVisitor) {}
 }
 
-impl<'mir, 'tcx: 'mir> TimeoutCallback<'mir, 'tcx> for Callback {
+impl<'mir, 'tcx: 'mir> MachineCallback<'mir, 'tcx> for Callback {
     fn call(&self, ecx: &mut MiriInterpCx<'mir, 'tcx>) -> InterpResult<'tcx> {
         ecx.unblock_thread(self.active_thread);
         Ok(())
diff --git a/src/tools/miri/src/shims/unix/linux/sync.rs b/src/tools/miri/src/shims/unix/linux/sync.rs
index 784fa12d18a..bbfb1c34db7 100644
--- a/src/tools/miri/src/shims/unix/linux/sync.rs
+++ b/src/tools/miri/src/shims/unix/linux/sync.rs
@@ -1,4 +1,4 @@
-use crate::concurrency::thread::{Time, TimeoutCallback};
+use crate::concurrency::thread::{MachineCallback, Time};
 use crate::*;
 use rustc_target::abi::{Align, Size};
 use std::time::SystemTime;
@@ -268,7 +268,7 @@ impl<'tcx> VisitMachineValues for Callback<'tcx> {
     }
 }
 
-impl<'mir, 'tcx: 'mir> TimeoutCallback<'mir, 'tcx> for Callback<'tcx> {
+impl<'mir, 'tcx: 'mir> MachineCallback<'mir, 'tcx> for Callback<'tcx> {
     fn call(&self, this: &mut MiriInterpCx<'mir, 'tcx>) -> InterpResult<'tcx> {
         this.unblock_thread(self.thread);
         this.futex_remove_waiter(self.addr_usize, self.thread);
diff --git a/src/tools/miri/src/shims/unix/sync.rs b/src/tools/miri/src/shims/unix/sync.rs
index cdb3cdc4b9a..72b71ada8e0 100644
--- a/src/tools/miri/src/shims/unix/sync.rs
+++ b/src/tools/miri/src/shims/unix/sync.rs
@@ -3,7 +3,7 @@ use std::time::SystemTime;
 use rustc_hir::LangItem;
 use rustc_middle::ty::{layout::TyAndLayout, query::TyCtxtAt, Ty};
 
-use crate::concurrency::thread::{Time, TimeoutCallback};
+use crate::concurrency::thread::{MachineCallback, Time};
 use crate::*;
 
 // pthread_mutexattr_t is either 4 or 8 bytes, depending on the platform.
@@ -901,7 +901,7 @@ impl<'tcx> VisitMachineValues for Callback<'tcx> {
     }
 }
 
-impl<'mir, 'tcx: 'mir> TimeoutCallback<'mir, 'tcx> for Callback<'tcx> {
+impl<'mir, 'tcx: 'mir> MachineCallback<'mir, 'tcx> for Callback<'tcx> {
     fn call(&self, ecx: &mut MiriInterpCx<'mir, 'tcx>) -> InterpResult<'tcx> {
         // We are not waiting for the condvar any more, wait for the
         // mutex instead.