Index: sys/kern/subr_rman.c
===================================================================
--- sys/kern/subr_rman.c
+++ sys/kern/subr_rman.c
@@ -524,7 +524,7 @@
 		DPRINTF(("truncated region: [%#jx, %#jx]; size %#jx (requested %#jx)\n",
 		       rstart, rend, (rend - rstart + 1), count));
 
-		if ((rend - rstart + 1) >= count) {
+		if ((rend - rstart) >= (count - 1)) {
 			DPRINTF(("candidate region: [%#jx, %#jx], size %#jx\n",
 			       rstart, rend, (rend - rstart + 1)));
 			if ((s->r_end - s->r_start + 1) == count) {