diff --git a/include/haproxy/backend-t.h b/include/haproxy/backend-t.h
index 8bee110..b5d448f 100644
--- a/include/haproxy/backend-t.h
+++ b/include/haproxy/backend-t.h
@@ -157,6 +157,7 @@
 	int   arg_opt1;			/* extra option 1 for the LB algo (algo-specific) */
 	int   arg_opt2;			/* extra option 2 for the LB algo (algo-specific) */
 	int   arg_opt3;			/* extra option 3 for the LB algo (algo-specific) */
+	int   arg_opt4;                 /* extra option 4 for the LB algo (algo-specific) */
 	__decl_thread(HA_RWLOCK_T lock);
 	struct server *fbck;		/* first backup server when !PR_O_USE_ALL_BK, or NULL */