--- src/openvpn/tun.c
+++ src/openvpn/tun.c
@@ -2054,6 +2054,11 @@
 
 #ifdef ENABLE_FEATURE_TUN_PERSIST
 
+/* TUNSETGROUP appeared in 2.6.23 */
+#ifndef TUNSETGROUP
+#define TUNSETGROUP _IOW('T', 206, int)
+#endif
+
 void
 tuncfg(const char *dev, const char *dev_type, const char *dev_node, int persist_mode, const char *username, const char *groupname, const struct tuntap_options *options)
 {