diff --git a/linux-user/syscall.c b/linux-user/syscall.c
index 81f79f994f31..de8918d629a6 100644
--- a/linux-user/syscall.c
+++ b/linux-user/syscall.c
@@ -7479,6 +7479,22 @@ abi_long do_syscall(void *cpu_env, int num, abi_long arg1,
             ret = get_errno(sys_sched_getaffinity(arg1, mask_size, mask));
 
             if (!is_error(ret)) {
+                if (ret > arg2) {
+                    /* More data returned than the caller's buffer will fit.
+                     * This only happens if sizeof(abi_long) < sizeof(long)
+                     * and the caller passed us a buffer holding an odd number
+                     * of abi_longs. If the host kernel is actually using the
+                     * extra 4 bytes then fail EINVAL; otherwise we can just
+                     * ignore them and only copy the interesting part.
+                     */
+                    int numcpus = sysconf(_SC_NPROCESSORS_CONF);
+                    if (numcpus > arg2 * 8) {
+                        ret = -TARGET_EINVAL;
+                        break;
+                    }
+                    ret = arg2;
+                }
+
                 if (copy_to_user(arg3, mask, ret)) {
                     goto efault;
                 }