diff --git a/src/libstrongswan/networking/tun_device.c b/src/libstrongswan/networking/tun_device.c
index 2191198e2..00de2eddf 100644
--- a/src/libstrongswan/networking/tun_device.c
+++ b/src/libstrongswan/networking/tun_device.c
@@ -390,14 +390,18 @@ static bool init_tun(private_tun_device_t *this, const char *name_tmpl)
 	/* this works on FreeBSD and might also work on Linux with older TUN
 	 * driver versions (no IFF_TUN) */
 	char devname[IFNAMSIZ];
-	int i;
+	/* the same process is allowed to open a device again, but that's not what
+	 * we want (unless we previously closed a device, which we don't know at
+	 * this point).  therefore, this counter is static so we don't accidentally
+	 * open a device twice */
+	static int i = -1;
 
 	if (name_tmpl)
 	{
 		DBG1(DBG_LIB, "arbitrary naming of TUN devices is not supported");
 	}
 
-	for (i = 0; i < 256; i++)
+	for (; ++i < 256; )
 	{
 		snprintf(devname, IFNAMSIZ, "/dev/tun%d", i);
 		this->tunfd = open(devname, O_RDWR);