diff --git a/src/mkfat.c b/src/mkfat.c
index 3753eb8..18c3439 100644
--- a/src/mkfat.c
+++ b/src/mkfat.c
@@ -29,6 +29,8 @@ int fat12_mkfs(struct pang_io *io, uint32_t bytes) {
     uint32_t fat_size_sectors = ((fat_size - 1) / sector_size) + 1;
 
     uint32_t root_directory_sector_count = cluster_size - (fat_size_sectors + reserved_sectors);
+    if (!root_directory_sector_count)
+        root_directory_sector_count = cluster_size;
     uint32_t root_directory_entry_count = (sector_size / sizeof(struct fat_directory_entry)) * root_directory_sector_count;
 
     fprintf(stderr, "bytes: %d\n", bytes);