diff --git a/sys/kern/kern_cpuset.c b/sys/kern/kern_cpuset.c
index 0723059544f..24c1ba826ce 100644
--- a/sys/kern/kern_cpuset.c
+++ b/sys/kern/kern_cpuset.c
@@ -1090,10 +1090,43 @@ cpuset_setproc_setthread(struct cpuset *tdset, struct cpuset *set,
 	if (error)
 		return (error);
 
-	return cpuset_shadow(tdset, nsetp, &mask, &domain, freelist,
+	return cpuset_shadow(set, nsetp, &mask, &domain, freelist,
 	    domainlist);
 }
 
+static int
+cpuset_setproc_newbase(struct thread *td, struct cpuset *set,
+    struct cpuset *nroot, struct cpuset **nsetp, struct domainlist *domainlist)
+{
+	struct domainset ndomain;
+	cpuset_t nmask;
+	struct cpuset *pbase;
+	int error;
+
+	pbase = cpuset_getbase(td->td_cpuset);
+
+	/* Copy process mask, then further apply the new root mask. */
+	CPU_COPY(&pbase->cs_mask, &nmask);
+	CPU_AND(&nmask, &nroot->cs_mask);
+
+	domainset_copy(pbase->cs_domain, &ndomain);
+	DOMAINSET_AND(&ndomain.ds_mask, &set->cs_domain->ds_mask);
+
+	/* Policy is too restrictive, will not work. */
+	if (CPU_EMPTY(&nmask) || DOMAINSET_EMPTY(&ndomain.ds_mask))
+		return (EDEADLK);
+
+	error = cpuset_create(&pbase, set, &nmask);
+	if (error != 0)
+		return (error);
+
+	/* Duplicates some work from above... oh well. */
+	pbase->cs_domain = domainset_shadow(set->cs_domain, &ndomain,
+	    domainlist);
+	*nsetp = pbase;
+	return (0);
+}
+
 /*
  * Handle three cases for updating an entire process.
  *
@@ -1115,10 +1148,10 @@ cpuset_setproc(pid_t pid, struct cpuset *set, cpuset_t *mask,
 	struct setlist freelist;
 	struct setlist droplist;
 	struct domainlist domainlist;
-	struct cpuset *nset;
+	struct cpuset *base, *nset, *nroot, *tdroot;
 	struct thread *td;
 	struct proc *p;
-	int threads;
+	int needed;
 	int nfree;
 	int error;
 
@@ -1134,21 +1167,41 @@ cpuset_setproc(pid_t pid, struct cpuset *set, cpuset_t *mask,
 	nfree = 1;
 	LIST_INIT(&droplist);
 	nfree = 0;
+	base = set;
+	nroot = NULL;
+	if (set != NULL)
+		nroot = cpuset_getroot(set);
 	for (;;) {
 		error = cpuset_which(CPU_WHICH_PID, pid, &p, &td, &nset);
 		if (error)
 			goto out;
-		if (nfree >= p->p_numthreads)
+		tdroot = cpuset_getroot(td->td_cpuset);
+		needed = p->p_numthreads;
+		if (set != NULL && tdroot != nroot)
+			needed++;
+		if (nfree >= needed)
 			break;
-		threads = p->p_numthreads;
 		PROC_UNLOCK(p);
-		if (nfree < threads) {
-			cpuset_freelist_add(&freelist, threads - nfree);
-			domainset_freelist_add(&domainlist, threads - nfree);
-			nfree = threads;
+		if (nfree < needed) {
+			cpuset_freelist_add(&freelist, needed - nfree);
+			domainset_freelist_add(&domainlist, needed - nfree);
+			nfree = needed;
 		}
 	}
 	PROC_LOCK_ASSERT(p, MA_OWNED);
+
+	/*
+	 * If we're changing roots and the root set is what has been specified
+	 * as the parent, then we'll create a new base with the process's mask
+	 * applied to it.
+	 */
+	if (set != NULL && nroot != tdroot) {
+		error = cpuset_setproc_newbase(td, set, nroot, &base,
+		    &domainlist);
+		if (error != 0)
+			goto unlock_out;
+	}
+
 	/*
 	 * Now that the appropriate locks are held and we have enough cpusets,
 	 * make sure the operation will succeed before applying changes. The
@@ -1159,7 +1212,7 @@ cpuset_setproc(pid_t pid, struct cpuset *set, cpuset_t *mask,
 		thread_lock(td);
 		if (set != NULL)
 			error = cpuset_setproc_test_setthread(td->td_cpuset,
-			    set);
+			    base);
 		else
 			error = cpuset_setproc_test_maskthread(td->td_cpuset,
 			    mask, domain);
@@ -1175,7 +1228,7 @@ cpuset_setproc(pid_t pid, struct cpuset *set, cpuset_t *mask,
 	FOREACH_THREAD_IN_PROC(p, td) {
 		thread_lock(td);
 		if (set != NULL)
-			error = cpuset_setproc_setthread(td->td_cpuset, set,
+			error = cpuset_setproc_setthread(td->td_cpuset, base,
 			    &nset, &freelist, &domainlist);
 		else
 			error = cpuset_setproc_maskthread(td->td_cpuset, mask,
@@ -1190,6 +1243,8 @@ cpuset_setproc(pid_t pid, struct cpuset *set, cpuset_t *mask,
 unlock_out:
 	PROC_UNLOCK(p);
 out:
+	if (base != NULL && base != set)
+		cpuset_rel(base);
 	while ((nset = LIST_FIRST(&droplist)) != NULL)
 		cpuset_rel_complete(nset);
 	cpuset_freelist_free(&freelist);