diff --git a/src/builtins/disown.rs b/src/builtins/disown.rs
index 41c4ef939..8c6408041 100644
--- a/src/builtins/disown.rs
+++ b/src/builtins/disown.rs
@@ -80,7 +80,6 @@ pub fn disown(parser: &Parser, streams: &mut IoStreams, args: &mut [&wstr]) -> O
             retval = STATUS_CMD_ERROR;
         }
     } else {
-        // TODO: This is supposed to be deduplicated or a hash set per comments below!
         let mut jobs = vec![];
 
         retval = STATUS_CMD_OK;
@@ -116,6 +115,11 @@ pub fn disown(parser: &Parser, streams: &mut IoStreams, args: &mut [&wstr]) -> O
             return retval;
         }
 
+        // One PID/JID may be repeated or multiple PIDs may refer to the same job;
+        // include the job only once.
+        jobs.sort_unstable_by_key(|job| job.job_id());
+        jobs.dedup_by_key(|job| job.job_id());
+
         // Disown all target jobs.
         for j in jobs {
             disown_job(cmd, streams, &j);
diff --git a/src/job_group.rs b/src/job_group.rs
index 9bb9ed432..709482154 100644
--- a/src/job_group.rs
+++ b/src/job_group.rs
@@ -12,7 +12,7 @@ use std::sync::{Arc, Mutex};
 #[repr(transparent)]
 pub struct JobId(NonZeroU32);
 
-#[derive(Clone, Copy, Debug, Eq, PartialEq)]
+#[derive(Clone, Copy, Debug, Eq, PartialEq, PartialOrd, Ord)]
 pub struct MaybeJobId(pub Option<JobId>);
 
 impl std::ops::Deref for MaybeJobId {