diff --git a/sys/vfs/msdosfs/msdosfs_fat.c b/sys/vfs/msdosfs/msdosfs_fat.c
--- a/sys/vfs/msdosfs/msdosfs_fat.c
+++ b/sys/vfs/msdosfs/msdosfs_fat.c
@@ -184,7 +184,8 @@
 		/*
 		 * Stop with all reserved clusters, not just with EOF.
 		 */
-		if ((cn | ~pmp->pm_fatmask) >= CLUST_RSRVD)
+		if ((cn | ~pmp->pm_fatmask) >= CLUST_RSRVD ||
+		    cn > pmp->pm_maxcluster)
 			goto hiteof;
 		byteoffset = FATOFS(pmp, cn);
 		fatblock(pmp, byteoffset, &bn, &bsize, &bo);