Index: sys/kern/kern_cpuset.c
===================================================================
--- sys/kern/kern_cpuset.c
+++ sys/kern/kern_cpuset.c
@@ -52,6 +52,7 @@
 #include <sys/sched.h>
 #include <sys/smp.h>
 #include <sys/syscallsubr.h>
+#include <sys/sysent.h>
 #include <sys/capsicum.h>
 #include <sys/cpuset.h>
 #include <sys/domainset.h>
@@ -1742,6 +1743,59 @@
 	return (0);
 }
 
+static int
+copyin_set(struct thread *td, const void *u, void *k, size_t size)
+{
+	int rv;
+	rv = copyin(u, k, size);
+
+	if (rv != 0)
+		return (rv);
+#if defined(__LP64__) && defined(COMPAT_FREEBSD32) && \
+    (__BYTE_ORDER__ == __ORDER_BIG_ENDIAN__)
+	struct bitset *kb = k;
+	if (SV_PROC_FLAG(td->td_proc, SV_ILP32)) {
+		/* Loop through swapping words. */
+		int *p = (int *)kb->__bits;
+		/* `size' is in bytes, we need bits. */
+		for (int i = 0; i < __bitset_words(size * 8); i++) {
+			int tmp = p[0];
+			p[0] = p[1];
+			p[1] = tmp;
+			p += 2;
+		}
+	}
+#endif
+	return (rv);
+}
+
+static int
+copyout_set(struct thread *td, const void *k, void *u, size_t size)
+{
+#if defined(__LP64__) && defined(COMPAT_FREEBSD32) && \
+    (__BYTE_ORDER__ == __ORDER_BIG_ENDIAN__)
+	const struct bitset *kb = k;
+	struct bitset *ub = u;
+	const int *kp = (const int *)kb->__bits;
+	int *up = (int *)ub->__bits;
+	int rv;
+
+	for (int i = 0; i < __bitset_words(CPU_SETSIZE); i++) {
+		/* `size' is in bytes, we need bits. */
+		for (int i = 0; i < __bitset_words(size * 8); i++) {
+			rv = suword32(up, kp[1]);
+			if (rv == 0)
+				rv = suword32(up + 1, kp[0]);
+			if (rv != 0)
+				return (rv);
+		}
+	}
+	return (0);
+#else
+	return (copyout(k, u, size));
+#endif
+}
+
 #ifndef _SYS_SYSPROTO_H_
 struct cpuset_args {
 	cpusetid_t	*setid;
@@ -1977,7 +2031,7 @@
 			goto out;
 		}
 		size = min(cpusetsize, sizeof(cpuset_t));
-		error = copyout(mask, maskp, size);
+		error = copyout_set(td, mask, maskp, size);
 		if (error != 0)
 			goto out;
 		if (cpusetsize > size) {
@@ -2117,7 +2171,7 @@
 
 	size = min(cpusetsize, sizeof(cpuset_t));
 	mask = malloc(sizeof(cpuset_t), M_TEMP, M_WAITOK | M_ZERO);
-	error = copyin(maskp, mask, size);
+	error = copyin_set(td, maskp, mask, size);
 	if (error)
 		goto out;
 	/*
@@ -2268,7 +2322,7 @@
 	}
 	DOMAINSET_COPY(&outset.ds_mask, mask);
 	if (error == 0)
-		error = copyout(mask, maskp, domainsetsize);
+		error = copyout_set(td, mask, maskp, domainsetsize);
 	if (error == 0)
 		if (suword32(policyp, outset.ds_policy) != 0)
 			error = EFAULT;
@@ -2318,7 +2372,7 @@
 		return (error);
 	memset(&domain, 0, sizeof(domain));
 	mask = malloc(domainsetsize, M_TEMP, M_WAITOK | M_ZERO);
-	error = copyin(maskp, mask, domainsetsize);
+	error = copyin_set(td, maskp, mask, domainsetsize);
 	if (error)
 		goto out;
 	/*