diff --git a/lib/libc/gen/getbsize.c b/lib/libc/gen/getbsize.c
index 277eeb454ae..7e88e3ff176 100644
--- a/lib/libc/gen/getbsize.c
+++ b/lib/libc/gen/getbsize.c
@@ -83,6 +83,7 @@ getbsize(headerlenp, blocksizep)
 		default:
 fmterr:			warnx("%s: unknown blocksize", p);
 			n = 512;
+			max = MAXB;
 			mul = 1;
 			break;
 		}