diff --git a/sysdep/linux/sysio.h b/sysdep/linux/sysio.h
index 56c3387d..dc807392 100644
--- a/sysdep/linux/sysio.h
+++ b/sysdep/linux/sysio.h
@@ -122,6 +122,8 @@ sysio_leave_group(sock *s, ip_addr maddr)
 #define TCP_MD5SIG  14
 #define TCP_MD5SIG_MAXKEYLEN 80
 
+#include <linux/types.h>
+
 struct tcp_md5sig {
   struct  sockaddr_storage tcpm_addr;             /* address associated */
   __u16   __tcpm_pad1;                            /* zero */