diff --git a/sys/net/ipfw3/ip_fw3.c b/sys/net/ipfw3/ip_fw3.c
--- a/sys/net/ipfw3/ip_fw3.c
+++ b/sys/net/ipfw3/ip_fw3.c
@@ -177,7 +177,11 @@
 		if (tmp->type == 0) {
 			tmp->type = 1;
 			tmp->id = module_id;
-			strncpy(tmp->name, module_name, strlen(module_name));
+			/* DF-0476: use strlcpy with the destination buffer size
+			 * instead of strncpy with the source length. The old
+			 * code overflowed name[20] when strlen(module_name) >= 20
+			 * and never wrote a NUL terminator. */
+			strlcpy(tmp->name, module_name, sizeof(tmp->name));
 			break;
 		}
 		tmp++;