Index: uspace/app/mkfat/mkfat.c
===================================================================
--- uspace/app/mkfat/mkfat.c	(revision 81e20c75433fb4887aa73c34e0befc7c58d0f4e6)
+++ uspace/app/mkfat/mkfat.c	(revision 7d364fb8ea8ef4fe1f9f9a2a7f89c21619faf824)
@@ -253,5 +253,6 @@
 		return ENOSPC;
 
-	fat_bytes = (cfg->total_clusters + 2) * FAT_SIZE(cfg->fat_type);
+	fat_bytes = div_round_up((cfg->total_clusters + 2) *
+	    FAT_CLUSTER_DOUBLE_SIZE(cfg->fat_type), 2);
 	cfg->fat_sectors = div_round_up(fat_bytes, cfg->sector_size);