diff --git a/src/helper/ioutil.c b/src/helper/ioutil.c
index d4f39e242..c103ce173 100644
--- a/src/helper/ioutil.c
+++ b/src/helper/ioutil.c
@@ -403,7 +403,7 @@ static int ioutil_Jim_Command_mac(Jim_Interp *interp, int argc,
 		{
 			if (strcmp("eth0", ifr->ifr_name) != 0)
 				continue;
-			strncpy(ifreq.ifr_name, ifr->ifr_name, sizeof(ifreq.ifr_name));
+			strncpy(ifreq.ifr_name, ifr->ifr_name, sizeof(ifreq.ifr_name) - 1);
 			if (ioctl(SockFD, SIOCGIFHWADDR, &ifreq) < 0) {
 				close(SockFD);
 				return JIM_ERR;