diff --git a/src/sample.c b/src/sample.c
index 21bbadd9a..f43a79ed3 100644
--- a/src/sample.c
+++ b/src/sample.c
@@ -1295,6 +1295,8 @@ int smp_resolve_args(struct proxy *p, char **err)
 		case ARGC_ACL:   ctx = "ACL keyword"; break;
 		case ARGC_SRV:   where = "in server directive in"; break;
 		case ARGC_SPOE:  where = "in spoe-message directive in"; break;
+		case ARGC_UBK:   where = "in use_backend expression in"; break;
+		case ARGC_USRV:  where = "in use-server expression in"; break;
 		case ARGC_HERR:  where = "in http-error directive in"; break;
 		case ARGC_OT:    where = "in ot-scope directive in"; break;
 		case ARGC_TCO:   where = "in tcp-request connection expression in"; break;