--- src/modules/rlm_sqlhpwippool/rlm_sqlhpwippool.c
+++ src/modules/rlm_sqlhpwippool/rlm_sqlhpwippool.c
@@ -771,7 +771,7 @@
 
 			nasip.s_addr = vp->vp_ipaddr;
 			strncpy(nasipstr, inet_ntoa(nasip), sizeof(nasipstr) - 1);
-			nasipstr[sizeof(nasipstr)] = 0;
+			nasipstr[sizeof(nasipstr) - 1] = 0;
 
 			if (!nvp_query(__LINE__, data, sqlsock,
 			    "UPDATE `%s`.`ips`, `radacct` "