diff --git a/src/proc.rs b/src/proc.rs
index 7bc817771..9f941856c 100644
--- a/src/proc.rs
+++ b/src/proc.rs
@@ -18,6 +18,7 @@ use crate::parser::{Block, Parser};
 use crate::reader::{fish_is_unwinding_for_exit, reader_schedule_prompt_repaint};
 use crate::redirection::RedirectionSpecList;
 use crate::signal::{signal_set_handlers_once, Signal};
+use crate::threads::MainThread;
 use crate::topic_monitor::{topic_monitor_principal, topic_t, GenerationsList};
 use crate::wait_handle::{InternalJobId, WaitHandle, WaitHandleRef, WaitHandleStore};
 use crate::wchar::{wstr, WString, L};
@@ -37,7 +38,7 @@ use std::io::{Read, Write};
 use std::os::fd::RawFd;
 use std::rc::Rc;
 use std::sync::atomic::{AtomicBool, AtomicI32, AtomicU64, AtomicU8, Ordering};
-use std::sync::{Arc, Mutex};
+use std::sync::Arc;
 
 /// Types of processes.
 #[derive(Default, Eq, PartialEq)]
@@ -1309,7 +1310,7 @@ pub fn hup_jobs(jobs: &JobList) {
 /// Add a job to the list of PIDs/PGIDs we wait on even though they are not associated with any
 /// jobs. Used to avoid zombie processes after disown.
 pub fn add_disowned_job(j: &Job) {
-    let mut disowned_pids = DISOWNED_PIDS.lock().unwrap();
+    let mut disowned_pids = DISOWNED_PIDS.get().borrow_mut();
     for process in j.processes().iter() {
         if process.has_pid() {
             disowned_pids.push(process.pid());
@@ -1319,7 +1320,7 @@ pub fn add_disowned_job(j: &Job) {
 
 // Reap any pids in our disowned list that have exited. This is used to avoid zombies.
 fn reap_disowned_pids() {
-    let mut disowned_pids = DISOWNED_PIDS.lock().unwrap();
+    let mut disowned_pids = DISOWNED_PIDS.get().borrow_mut();
     // waitpid returns 0 iff the PID/PGID in question has not changed state; remove the pid/pgid
     // if it has changed or an error occurs (presumably ECHILD because the child does not exist)
     disowned_pids.retain(|pid| {
@@ -1334,7 +1335,8 @@ fn reap_disowned_pids() {
 
 /// A list of pids that have been disowned. They are kept around until either they exit or
 /// we exit. Poll these from time-to-time to prevent zombie processes from happening (#5342).
-static DISOWNED_PIDS: Mutex<Vec<libc::pid_t>> = Mutex::new(Vec::new());
+static DISOWNED_PIDS: MainThread<RefCell<Vec<libc::pid_t>>> =
+    MainThread::new(RefCell::new(Vec::new()));
 
 /// See if any reapable processes have exited, and mark them accordingly.
 /// \param block_ok if no reapable processes have exited, block until one is (or until we receive a