diff --git a/source/fs/mufs/super.c b/source/fs/mufs/super.c
index 1a91772..31bdda8 100644
--- a/source/fs/mufs/super.c
+++ b/source/fs/mufs/super.c
@@ -60,11 +60,25 @@ void mufs_unmount(struct mufs *fs)
 
 int mufs_format(struct flash_dev *dev)
 {
+	struct mufs fs;
 	struct mufs_super super;
+	uint8_t log2_bits_per_block = dev->log2_block_size + ilog2(8);
+	size_t nbitmap_size;
+	uint32_t block;
+
+	fs.dev = dev;
+	fs.nblocks = flash_get_capacity(dev) >> dev->log2_block_size;
+	nbitmap_size = align_up(fs.nblocks, log2_bits_per_block) >>
+		log2_bits_per_block;
+
+	flash_erase(dev, 1, nbitmap_size);
+
+	for (block = 0; block < 1 + nbitmap_size; ++block)
+		mufs_mark_block(&fs, block, 1);
 
 	memcpy(super.magic, "mufs", 4);
 
-	super.nblocks = flash_get_capacity(dev) >> dev->log2_block_size;
+	super.nblocks = fs.nblocks;
 
 	super.root.file_size = 0;
 	super.root.root = 0;