diff --git a/sys/netgraph/ng_sample.c b/sys/netgraph/ng_sample.c
index 4bb4684b846..93eb736c7b5 100644
--- a/sys/netgraph/ng_sample.c
+++ b/sys/netgraph/ng_sample.c
@@ -203,7 +203,7 @@ ng_xxx_newhook(node_p node, hook_p hook, const char *name)
 	    NG_XXX_HOOK_DLCI_LEADIN, strlen(NG_XXX_HOOK_DLCI_LEADIN)) == 0) {
 		char *eptr;
 
-		cp = name + sizeof(NG_XXX_HOOK_DLCI_LEADIN);
+		cp = name + strlen(NG_XXX_HOOK_DLCI_LEADIN);
 		if (!isdigit(*cp) || (cp[0] == '0' && cp[1] != '\0'))
 			return (EINVAL);
 		dlci = (int)strtoul(cp, &eptr, 10);