diff --git a/sys/arm64/arm64/gicv3_its.c b/sys/arm64/arm64/gicv3_its.c
--- a/sys/arm64/arm64/gicv3_its.c
+++ b/sys/arm64/arm64/gicv3_its.c
@@ -801,7 +801,7 @@
 		/* Make sure changes are observable my the GIC */
 		dsb(sy);
 
-		size = (flsl(LPI_CONFTAB_SIZE | GIC_FIRST_LPI) - 1);
+		size = (flsl(LPI_CONFTAB_SIZE | GIC_FIRST_LPI) - 2);
 
 		xbaser = vtophys(sc->sc_conf_base) |
 		    (GICR_PROPBASER_SHARE_IS << GICR_PROPBASER_SHARE_SHIFT) |