diff --git a/libraries/libmdb/mdb.c b/libraries/libmdb/mdb.c
index d44b1ec..e13f861 100644
--- a/libraries/libmdb/mdb.c
+++ b/libraries/libmdb/mdb.c
@@ -1478,7 +1478,7 @@ mdb_env_sync(MDB_env *env, int force)
 	int rc = 0;
 	if (force || !F_ISSET(env->me_flags, MDB_NOSYNC)) {
 		if (env->me_flags & MDB_WRITEMAP) {
-			int flags = (env->me_flags & MDB_MAPSYNC) ? MS_SYNC : MS_ASYNC;
+			int flags = (env->me_flags & MDB_MAPASYNC) ? MS_ASYNC : MS_SYNC;
 			if (MDB_MSYNC(env->me_map, env->me_mapsize, flags))
 				rc = ErrCode();
 #ifdef _WIN32
@@ -2383,7 +2383,7 @@ mdb_env_write_meta(MDB_txn *txn)
 		mp->mm_last_pg = txn->mt_next_pgno - 1;
 		mp->mm_txnid = txn->mt_txnid;
 		if (!(env->me_flags & (MDB_NOMETASYNC|MDB_NOSYNC))) {
-			rc = (env->me_flags & MDB_MAPSYNC) ? MS_SYNC : MS_ASYNC;
+			rc = (env->me_flags & MDB_MAPASYNC) ? MS_ASYNC : MS_SYNC;
 			ptr = env->me_map;
 			if (toggle)
 				ptr += env->me_psize;
diff --git a/libraries/libmdb/mdb.h b/libraries/libmdb/mdb.h
index 8eefc7d..4430c58 100644
--- a/libraries/libmdb/mdb.h
+++ b/libraries/libmdb/mdb.h
@@ -163,8 +163,8 @@ typedef void (MDB_rel_func)(MDB_val *item, void *oldptr, void *newptr, void *rel
 #define MDB_NOMETASYNC		0x40000
 	/** use writable mmap */
 #define MDB_WRITEMAP		0x80000
-	/** use synchronous msync */
-#define MDB_MAPSYNC		0x100000
+	/** use asynchronous msync */
+#define MDB_MAPASYNC		0x100000
 /** @} */
 
 /**	@defgroup	mdb_open	Database Flags