diff --git a/lib/libthr/thread/thr_attr.c b/lib/libthr/thread/thr_attr.c
index 7fe500346275..bc8eabb3c223 100644
--- a/lib/libthr/thread/thr_attr.c
+++ b/lib/libthr/thread/thr_attr.c
@@ -574,13 +574,14 @@ _get_kern_cpuset_size(void)
 
 	if (kern_cpuset_size == 0) {
 		size_t len;
+		int maxcpus;
 
-		len = sizeof(kern_cpuset_size);
-		if (sysctlbyname("kern.smp.maxcpus", &kern_cpuset_size,
-		    &len, NULL, 0))
+		len = sizeof(maxcpus);
+		if (sysctlbyname("kern.smp.maxcpus", &maxcpus, &len, NULL, 0))
 			PANIC("failed to get sysctl kern.smp.maxcpus");
-
-		kern_cpuset_size = (kern_cpuset_size + 7) / 8;
+		int nbits_long = sizeof(long) * NBBY;
+		int num_long = (maxcpus + nbits_long - 1) / nbits_long;
+		kern_cpuset_size = num_long * sizeof(long);
 	}
 
 	return (kern_cpuset_size);
diff --git a/sys/kern/kern_cpuset.c b/sys/kern/kern_cpuset.c
index b4601f13e9bf..23aa9df5e6e2 100644
--- a/sys/kern/kern_cpuset.c
+++ b/sys/kern/kern_cpuset.c
@@ -889,10 +889,6 @@ cpuset_getaffinity(struct thread *td, struct cpuset_getaffinity_args *uap)
 	int error;
 	size_t size;
 
-	if (uap->cpusetsize == 0) {
-		td->td_retval[0] = sizeof(cpuset_t);
-		return (0);
-	}
 	if (uap->cpusetsize < sizeof(cpuset_t) ||
 	    uap->cpusetsize > CPU_MAXSIZE / NBBY)
 		return (ERANGE);