diff --git a/lib/libthr/thread/thr_attr.c b/lib/libthr/thread/thr_attr.c
--- a/lib/libthr/thread/thr_attr.c
+++ b/lib/libthr/thread/thr_attr.c
@@ -599,9 +599,9 @@
 		size_t len;
 
 		len = sizeof(kern_cpuset_size);
-		if (sysctlbyname("kern.sched.cpusetsize", &kern_cpuset_size,
+		if (sysctlbyname("kern.sched.cpusetsizemin", &kern_cpuset_size,
 		    &len, NULL, 0))
-			PANIC("failed to get sysctl kern.sched.cpusetsize");
+			PANIC("failed to get sysctl kern.sched.cpusetsizemin");
 	}
 
 	return (kern_cpuset_size);
diff --git a/sys/kern/kern_cpuset.c b/sys/kern/kern_cpuset.c
--- a/sys/kern/kern_cpuset.c
+++ b/sys/kern/kern_cpuset.c
@@ -141,11 +141,27 @@
 SYSCTL_INT(_kern_sched, OID_AUTO, cpusetsize, CTLFLAG_RD | CTLFLAG_CAPRD,
     SYSCTL_NULL_INT_PTR, sizeof(cpuset_t), "sizeof(cpuset_t)");
 
+static int sysctl_kern_sched_cpusetsizemin(SYSCTL_HANDLER_ARGS);
+
+/* Return the minimum size of cpuset_t allowed by the kernel */
+SYSCTL_PROC(_kern_sched, OID_AUTO, cpusetsizemin, CTLFLAG_RD | CTLFLAG_CAPRD |
+    CTLTYPE_INT | CTLFLAG_MPSAFE, NULL, 0, sysctl_kern_sched_cpusetsizemin, "I",
+    "The minimum size of cpuset_t allowed by the kernel");
+
 cpuset_t *cpuset_root;
 cpuset_t cpuset_domain[MAXMEMDOM];
 
 static int domainset_valid(const struct domainset *, const struct domainset *);
 
+static int
+sysctl_kern_sched_cpusetsizemin(SYSCTL_HANDLER_ARGS)
+{
+	int cpusetsize;
+
+	cpusetsize = howmany(mp_maxid, NBBY);
+	return (SYSCTL_OUT(req, &cpusetsize, sizeof(cpusetsize)));
+}
+
 /*
  * Find the first non-anonymous set starting from 'set'.
  */