diff --git a/lmdb-sys/lmdb/libraries/liblmdb/mdb.c b/lmdb-sys/lmdb/libraries/liblmdb/mdb.c
index a7a27f2..51b1484 100644
--- a/lmdb-sys/lmdb/libraries/liblmdb/mdb.c
+++ b/lmdb-sys/lmdb/libraries/liblmdb/mdb.c
@@ -96,6 +96,7 @@ static NtCloseFunc *NtClose;
 #  define SSIZE_MAX	INT_MAX
 # endif
 #endif
+#define MDB_OFF_T	int64_t
 #else
 #include <sys/types.h>
 #include <sys/stat.h>
@@ -108,6 +109,7 @@ static NtCloseFunc *NtClose;
 #include <sys/file.h>
 #endif
 #include <fcntl.h>
+#define MDB_OFF_T	off_t
 #endif
 
 #if defined(__mips) && defined(__linux)
@@ -1507,7 +1509,7 @@ struct MDB_env {
 	MDB_txn		*me_txn;		/**< current write transaction */
 	MDB_txn		*me_txn0;		/**< prealloc'd write transaction */
 	mdb_size_t	me_mapsize;		/**< size of the data memory map */
-	off_t		me_size;		/**< current file size */
+	MDB_OFF_T	me_size;		/**< current file size */
 	pgno_t		me_maxpg;		/**< me_mapsize / me_psize */
 	MDB_dbx		*me_dbxs;		/**< array of static DB info */
 	uint16_t	*me_dbflags;	/**< array of flags from MDB_db.md_flags */
@@ -3668,7 +3670,7 @@ mdb_page_flush(MDB_txn *txn, int keep)
 	unsigned	psize = env->me_psize, j;
 	int			i, pagecount = dl[0].mid, rc;
 	size_t		size = 0;
-	off_t		pos = 0;
+	MDB_OFF_T	pos = 0;
 	pgno_t		pgno = 0;
 	MDB_page	*dp = NULL;
 #ifdef _WIN32
@@ -3676,7 +3678,7 @@ mdb_page_flush(MDB_txn *txn, int keep)
 #else
 	struct iovec iov[MDB_COMMIT_PAGES];
 	ssize_t		wsize = 0, wres;
-	off_t		wpos = 0, next_pos = 1; /* impossible pos, so pos != next_pos */
+	MDB_OFF_T	wpos = 0, next_pos = 1; /* impossible pos, so pos != next_pos */
 	int			n = 0;
 #endif
 
@@ -4240,7 +4242,7 @@ mdb_env_write_meta(MDB_txn *txn)
 	MDB_meta	meta, metab, *mp;
 	unsigned flags;
 	mdb_size_t mapsize;
-	off_t off;
+	MDB_OFF_T off;
 	int rc, len, toggle;
 	char *ptr;
 	HANDLE mfd;
@@ -5229,7 +5231,7 @@ mdb_env_setup_locks(MDB_env *env, MDB_name *fname, int mode, int *excl)
 	union semun semu;
 #endif
 	int rc;
-	off_t size, rsize;
+	MDB_OFF_T size, rsize;
 
 	rc = mdb_fopen(env, fname, MDB_O_LOCKS, mode, &env->me_lfd);
 	if (rc) {
@@ -6097,7 +6099,7 @@ mdb_rpage_get(MDB_txn *txn, pgno_t pg0, MDB_page **ret)
 		len, &off, &len, ViewUnmap, (env->me_flags & MDB_RDONLY) ? 0 : MEM_RESERVE, PAGE_READONLY); \
 	if (rc) rc = mdb_nt2win32(rc)
 #else
-	off_t off;
+	MDB_OFF_T off;
 	size_t len;
 #define SET_OFF(off,val)	off = val
 #define MAP(rc,env,addr,len,off)	\