diff --git a/unix/sockcmsg_unix.go b/unix/sockcmsg_unix.go
index 70af5a72..f1493a3e 100644
--- a/unix/sockcmsg_unix.go
+++ b/unix/sockcmsg_unix.go
@@ -62,7 +62,7 @@ func ParseSocketControlMessage(b []byte) ([]SocketControlMessage, error) {
 
 func socketControlMessageHeaderAndData(b []byte) (*Cmsghdr, []byte, error) {
 	h := (*Cmsghdr)(unsafe.Pointer(&b[0]))
-	if h.Len < SizeofCmsghdr || int(h.Len) > len(b) {
+	if h.Len < SizeofCmsghdr || uint64(h.Len) > uint64(len(b)) {
 		return nil, nil, EINVAL
 	}
 	return h, b[cmsgAlignOf(SizeofCmsghdr):h.Len], nil