diff --git a/source/fs/mufs/block.c b/source/fs/mufs/block.c
index 30d896a..0cce7d0 100644
--- a/source/fs/mufs/block.c
+++ b/source/fs/mufs/block.c
@@ -6,68 +6,82 @@
 
 #include "block.h"
 
-static int mufs_mark_block(struct mufs *fs, uint32_t block, int status)
+int mufs_mark_block(struct mufs *fs, uint32_t block, int status)
 {
-	char data[1 << fs->dev->log2_block_size];
-	uint8_t log2_bits_per_block = fs->dev->log2_block_size + ilog2(8);
-	size_t index;
+	struct flash_dev *dev = fs->dev;
+	uint32_t data;
+	size_t offset, index;
 
-	index = block & ((UINT32_C(1) << log2_bits_per_block) - 1);
-	block >>= log2_bits_per_block;
+	if (block >= fs->nblocks)
+		return -1;
 
-	if (flash_read(fs->dev, (1 + block) << fs->dev->log2_block_size, data,
-		sizeof data) == 0)
+	offset = align(block >> ilog2(8), ilog2(4));
+	index = mask(block, ilog2(8) + ilog2(4));
+
+	if (flash_read(fs->dev, (1 << dev->log2_block_size) + offset, &data,
+		sizeof data) ==0)
 		return -1;
 
 	if (status) {
-		set_bit(data, index);
+		data |= 1 << index;
 	} else {
-		clear_bit(data, index);
+		data = data & ~(1 << index);
 	}
 
-	if (flash_write(fs->dev, (1 + block) << fs->dev->log2_block_size, data,
+	if (flash_write(fs->dev, (1 << dev->log2_block_size) + offset, &data,
 		sizeof data) == 0)
 		return -1;
 
 	return 0;
 }
 
-int mufs_alloc_block(struct mufs *fs, uint32_t *found)
+static size_t mufs_next_free_block(struct mufs *fs)
 {
-	char data[1 << fs->dev->log2_block_size];
-	uint32_t nblocks = fs->nblocks;
-	uint32_t nbits;
-	uint32_t block = 0;
-	size_t index;
-	uint8_t log2_bits_per_block = fs->dev->log2_block_size + ilog2(8);
-	size_t nbitmap_size = align_up(fs->nblocks, log2_bits_per_block) >>
-		log2_bits_per_block;
+	struct flash_dev *dev = fs->dev;
+	char data[32];
+	size_t nblocks = fs->nblocks;
+	size_t offset, index, bitlen, len;
+
+	offset = 0;
 
 	while (nblocks) {
-		if (flash_read(fs->dev, (1 + block) << fs->dev->log2_block_size, data,
-			sizeof data) == 0)
-			return -1;
+		bitlen = min(BIT_SIZE(data), nblocks);
+		len = bitlen >> ilog2(8);
 
-		nbits = min(nblocks, UINT32_C(1) << log2_bits_per_block);
+		if (flash_read(fs->dev, (1 << dev->log2_block_size) + offset, data,
+			len) == 0)
+			return SIZE_MAX;
 
-		if ((index = next_clear_bit(data, nbits)) == SIZE_MAX) {
-			++block;
-			nblocks -= nbits;
-			continue;
-		}
+		if ((index = next_clear_bit(data, bitlen)) != SIZE_MAX)
+			return (offset >> (ilog2(8) + ilog2(32))) + index;
 
-		index += block << log2_bits_per_block;
-		*found = 1 + nbitmap_size + index;
+		if (flash_write(fs->dev, (1 << dev->log2_block_size) + offset, data,
+			len) == 0)
+			return SIZE_MAX;
 
-		return mufs_mark_block(fs, index, 1);
+		offset += len;
+		nblocks -= bitlen;
 	}
 
-	return -1;
+	return SIZE_MAX;
+}
+
+int mufs_alloc_block(struct mufs *fs, uint32_t *found)
+{
+	size_t index;
+
+	if ((index = mufs_next_free_block(fs)) == SIZE_MAX)
+		return -1;
+
+	*found = index;
+
+	return mufs_mark_block(fs, index, 1);
 }
 
 int mufs_free_block(struct mufs *fs, uint32_t block)
 {
-	uint8_t log2_bits_per_block = fs->dev->log2_block_size + ilog2(8);
+	struct flash_dev *dev = fs->dev;
+	uint8_t log2_bits_per_block = dev->log2_block_size + ilog2(8);
 	size_t nbitmap_size = align_up(fs->nblocks, log2_bits_per_block) >>
 		log2_bits_per_block;
 
@@ -76,5 +90,5 @@ int mufs_free_block(struct mufs *fs, uint32_t block)
 
 	flash_erase(fs->dev, block, 1);
 
-	return mufs_mark_block(fs, block - 1 - nbitmap_size, 0);
+	return mufs_mark_block(fs, block, 0);
 }
diff --git a/source/fs/mufs/block.h b/source/fs/mufs/block.h
index fc9f2b4..a3c1355 100644
--- a/source/fs/mufs/block.h
+++ b/source/fs/mufs/block.h
@@ -1,4 +1,5 @@
 #pragma once
 
+int mufs_mark_block(struct mufs *fs, uint32_t block, int status);
 int mufs_alloc_block(struct mufs *fs, uint32_t *block);
 int mufs_free_block(struct mufs *fs, uint32_t block);