diff --git a/minix/include/minix/libminixfs.h b/minix/include/minix/libminixfs.h
index 20fff4152..8b361aa84 100644
--- a/minix/include/minix/libminixfs.h
+++ b/minix/include/minix/libminixfs.h
@@ -13,8 +13,8 @@ struct buf {
   struct buf *lmfs_next;       /* used to link all free bufs in a chain */
   struct buf *lmfs_prev;       /* used to link all free bufs the other way */
   struct buf *lmfs_hash;       /* used to link bufs on hash chains */
-  block_t lmfs_blocknr;        /* block number of its (minor) device */
   dev_t lmfs_dev;              /* major | minor device where block resides */
+  block64_t lmfs_blocknr;      /* block number of its (minor) device */
   char lmfs_count;             /* number of users of this buffer */
   char lmfs_needsetcache;      /* to be identified to VM */
   unsigned int lmfs_bytes;     /* Number of bytes allocated in bp */
@@ -42,8 +42,8 @@ void lmfs_set_blocksize(int blocksize, int major);
 void lmfs_reset_rdwt_err(void); 
 int lmfs_rdwt_err(void); 
 void lmfs_buf_pool(int new_nr_bufs);
-struct buf *lmfs_get_block(dev_t dev, block_t block,int only_search);
-struct buf *lmfs_get_block_ino(dev_t dev, block_t block,int only_search,
+struct buf *lmfs_get_block(dev_t dev, block64_t block,int only_search);
+struct buf *lmfs_get_block_ino(dev_t dev, block64_t block,int only_search,
 	ino_t ino, u64_t off);
 void lmfs_invalidate(dev_t device);
 void lmfs_put_block(struct buf *bp, int block_type);
diff --git a/minix/lib/libminixfs/bio.c b/minix/lib/libminixfs/bio.c
index 5b47e8f8f..8f0b72aa4 100644
--- a/minix/lib/libminixfs/bio.c
+++ b/minix/lib/libminixfs/bio.c
@@ -56,7 +56,7 @@ lmfs_driver(dev_t dev, char *label)
  * TODO: limit according to the number of available buffers.
  */
 static void
-block_prefetch(dev_t dev, block_t block, block_t nblocks)
+block_prefetch(dev_t dev, block64_t block, unsigned int nblocks)
 {
 	struct buf *bp, *bufs[NR_IOREQS];
 	unsigned int count;
@@ -103,8 +103,9 @@ ssize_t
 lmfs_bio(dev_t dev, struct fsdriver_data * data, size_t bytes, off_t pos,
 	int call)
 {
-	block_t block, blocks_left;
+	block64_t block;
 	size_t block_size, off, block_off, chunk;
+	unsigned int blocks_left;
 	struct buf *bp;
 	int r, write, how;
 
@@ -116,8 +117,10 @@ lmfs_bio(dev_t dev, struct fsdriver_data * data, size_t bytes, off_t pos,
 
 	assert(block_size > 0);
 
-	/* FIXME: block_t is 32-bit, so we have to impose a limit here. */
-	if (pos < 0 || pos / block_size > UINT32_MAX || bytes > SSIZE_MAX)
+	if (bytes == 0)
+		return 0; /* just in case */
+
+	if (pos < 0 || bytes > SSIZE_MAX || pos > INT64_MAX - bytes + 1)
 		return EINVAL;
 
 	off = 0;
diff --git a/minix/lib/libminixfs/cache.c b/minix/lib/libminixfs/cache.c
index 408c26175..9c6533d54 100644
--- a/minix/lib/libminixfs/cache.c
+++ b/minix/lib/libminixfs/cache.c
@@ -18,7 +18,7 @@
 #include <minix/u64.h>
 #include <minix/bdev.h>
 
-#define BUFHASH(b) ((b) % nr_bufs)
+#define BUFHASH(b) ((unsigned int)((b) % nr_bufs))
 #define MARKCLEAN  lmfs_markclean
 
 #define MINBUFS 6 	/* minimal no of bufs for sanity check */
@@ -178,8 +178,7 @@ static void lmfs_alloc_block(struct buf *bp)
 /*===========================================================================*
  *				lmfs_get_block				     *
  *===========================================================================*/
-struct buf *lmfs_get_block(register dev_t dev, register block_t block,
-	int only_search)
+struct buf *lmfs_get_block(dev_t dev, block64_t block, int only_search)
 {
 	return lmfs_get_block_ino(dev, block, only_search, VMC_NO_INODE, 0);
 }
@@ -243,7 +242,7 @@ static void freeblock(struct buf *bp)
 /*===========================================================================*
  *				lmfs_get_block_ino			     *
  *===========================================================================*/
-struct buf *lmfs_get_block_ino(dev_t dev, block_t block, int only_search,
+struct buf *lmfs_get_block_ino(dev_t dev, block64_t block, int only_search,
 	ino_t ino, u64_t ino_off)
 {
 /* Check to see if the requested block is in the block cache.  If so, return
@@ -263,7 +262,7 @@ struct buf *lmfs_get_block_ino(dev_t dev, block_t block, int only_search,
 
   int b;
   static struct buf *bp;
-  u64_t dev_off = (u64_t) block * fs_block_size;
+  uint64_t dev_off;
   struct buf *prev_ptr;
 
   assert(buf_hash);
@@ -274,6 +273,10 @@ struct buf *lmfs_get_block_ino(dev_t dev, block_t block, int only_search,
 
   assert(dev != NO_DEV);
 
+  assert(block <= UINT64_MAX / fs_block_size);
+
+  dev_off = block * fs_block_size;
+
   if((ino_off % fs_block_size)) {
 
 	printf("cache: unaligned lmfs_get_block_ino ino_off %llu\n",
@@ -424,14 +427,14 @@ void lmfs_put_block(
  * disk immediately if they are dirty.
  */
   dev_t dev;
-  off_t dev_off;
+  uint64_t dev_off;
   int r;
 
   if (bp == NULL) return;	/* it is easier to check here than in caller */
 
   dev = bp->lmfs_dev;
 
-  dev_off = (off_t) bp->lmfs_blocknr * fs_block_size;
+  dev_off = bp->lmfs_blocknr * fs_block_size;
 
   lowercount(bp);
   if (bp->lmfs_count != 0) return;	/* block is still in use */
@@ -535,8 +538,8 @@ static void read_block(
   		BDEV_NOFLAGS);
   }
   if (r < 0) {
-  	printf("fs cache: I/O error on device %d/%d, block %u\n",
-  	major(dev), minor(dev), bp->lmfs_blocknr);
+	printf("fs cache: I/O error on device %d/%d, block %"PRIu64"\n",
+	    major(dev), minor(dev), bp->lmfs_blocknr);
   	op_failed = 1;
   } else if (r != (ssize_t) fs_block_size) {
   	r = END_OF_FILE;
@@ -679,7 +682,7 @@ void lmfs_rw_scattered(
 		int p;
 		vir_bytes vdata, blockrem;
 		bp = bufq[nblocks];
-		if (bp->lmfs_blocknr != (block_t) bufq[0]->lmfs_blocknr + nblocks)
+		if (bp->lmfs_blocknr != bufq[0]->lmfs_blocknr + nblocks)
 			break;
 		if(niovecs >= NR_IOREQS-iov_per_block) break;
 		vdata = (vir_bytes) bp->data;
@@ -710,8 +713,9 @@ void lmfs_rw_scattered(
 	 * may have done less than what we asked for.
 	 */
 	if (r < 0) {
-		printf("fs cache: I/O error %d on device %d/%d, block %u\n",
-			r, major(dev), minor(dev), bufq[0]->lmfs_blocknr);
+		printf("fs cache: I/O error %d on device %d/%d, "
+		    "block %"PRIu64"\n",
+		    r, major(dev), minor(dev), bufq[0]->lmfs_blocknr);
 	}
 	for (i = 0; i < nblocks; i++) {
 		bp = bufq[i];
diff --git a/sys/sys/types.h b/sys/sys/types.h
index b3657d494..aea1867f1 100644
--- a/sys/sys/types.h
+++ b/sys/sys/types.h
@@ -118,6 +118,7 @@ typedef int64_t		i64_t;
 /* some Minix specific types that do not conflict with posix */
 typedef uint32_t zone_t;      /* zone number */
 typedef uint32_t block_t;     /* block number */
+typedef uint64_t block64_t;   /* block number, 64-bit */
 typedef uint32_t bit_t;       /* bit number in a bit map */
 typedef uint16_t zone1_t;     /* zone number for V1 file systems */
 typedef uint32_t bitchunk_t; /* collection of bits in a bitmap */