diff --git a/libraries/liblmdb/mdb.c b/libraries/liblmdb/mdb.c
index 8c69e9f..0e2e227 100644
--- a/libraries/liblmdb/mdb.c
+++ b/libraries/liblmdb/mdb.c
@@ -1080,12 +1080,16 @@ struct MDB_txn {
  *	@ingroup internal
  *	@{
  */
-#define MDB_TXN_RDONLY		0x01		/**< read-only transaction */
+	/** #mdb_txn_begin() flags */
+#define MDB_TXN_BEGIN_FLAGS	(MDB_NOMETASYNC|MDB_NOSYNC|MDB_RDONLY)
+#define MDB_TXN_NOMETASYNC	MDB_NOMETASYNC	/**< don't sync meta for this txn on commit */
+#define MDB_TXN_NOSYNC		MDB_NOSYNC	/**< don't sync this txn on commit */
+#define MDB_TXN_RDONLY		MDB_RDONLY	/**< read-only transaction */
+	/* internal txn flags */
+#define MDB_TXN_WRITEMAP	MDB_WRITEMAP	/**< copy of #MDB_env flag in writers */
 #define MDB_TXN_ERROR		0x02		/**< txn is unusable after an error */
 #define MDB_TXN_DIRTY		0x04		/**< must write, even if dirty list is empty */
 #define MDB_TXN_SPILLS		0x08		/**< txn or a parent has spilled pages */
-#define MDB_TXN_NOSYNC		0x10		/**< don't sync this txn on commit */
-#define MDB_TXN_NOMETASYNC	0x20		/**< don't sync meta for this txn on commit */
 /** @} */
 	unsigned int	mt_flags;		/**< @ref mdb_txn */
 	/** #dirty_list room: Array size - \#dirty pages visible to this txn.
@@ -1996,7 +2000,7 @@ mdb_page_dirty(MDB_txn *txn, MDB_page *mp)
 	MDB_ID2 mid;
 	int rc, (*insert)(MDB_ID2L, MDB_ID2 *);
 
-	if (txn->mt_env->me_flags & MDB_WRITEMAP) {
+	if (txn->mt_flags & MDB_TXN_WRITEMAP) {
 		insert = mdb_mid2l_append;
 	} else {
 		insert = mdb_mid2l_insert;
@@ -2570,7 +2574,7 @@ mdb_txn_renew0(MDB_txn *txn)
 	int rc, new_notls = 0;
 
 	if (txn->mt_flags & MDB_TXN_RDONLY) {
-		txn->mt_flags = MDB_TXN_RDONLY;
+		txn->mt_flags &= MDB_TXN_BEGIN_FLAGS;
 		/* Setup db info */
 		txn->mt_numdbs = env->me_numdbs;
 		txn->mt_dbxs = env->me_dbxs;	/* mostly static anyway */
@@ -2720,18 +2724,20 @@ mdb_txn_begin(MDB_env *env, MDB_txn *parent, unsigned int flags, MDB_txn **ret)
 	MDB_ntxn *ntxn;
 	int rc, size, tsize = sizeof(MDB_txn);
 
+	flags &= MDB_TXN_BEGIN_FLAGS;
+	flags |= env->me_flags & MDB_WRITEMAP;
+
 	if (env->me_flags & MDB_FATAL_ERROR) {
 		DPUTS("environment had fatal error, must shutdown!");
 		return MDB_PANIC;
 	}
-	if ((env->me_flags & MDB_RDONLY) && !(flags & MDB_RDONLY))
+	if (env->me_flags & MDB_RDONLY & ~flags) /* write txn in RDONLY env */
 		return EACCES;
 	if (parent) {
 		/* Nested transactions: Max 1 child, write txns only, no writemap */
 		if (parent->mt_child ||
-			(flags & MDB_RDONLY) ||
-			(parent->mt_flags & (MDB_TXN_RDONLY|MDB_TXN_ERROR)) ||
-			(env->me_flags & MDB_WRITEMAP))
+			((flags | parent->mt_flags) &
+			 (MDB_RDONLY|MDB_WRITEMAP|MDB_TXN_ERROR)))
 		{
 			return (parent->mt_flags & MDB_TXN_RDONLY) ? EINVAL : MDB_BAD_TXN;
 		}
@@ -2754,14 +2760,9 @@ mdb_txn_begin(MDB_env *env, MDB_txn *parent, unsigned int flags, MDB_txn **ret)
 	}
 	txn->mt_dbs = (MDB_db *) ((char *)txn + tsize);
 	if (flags & MDB_RDONLY) {
-		txn->mt_flags |= MDB_TXN_RDONLY;
 		txn->mt_dbflags = (unsigned char *)(txn->mt_dbs + env->me_maxdbs);
 		txn->mt_dbiseqs = env->me_dbiseqs;
 	} else {
-		if (flags & MDB_NOSYNC)
-			txn->mt_flags |= MDB_TXN_NOSYNC;
-		if (flags & MDB_NOMETASYNC)
-			txn->mt_flags |= MDB_TXN_NOMETASYNC;
 		txn->mt_cursors = (MDB_cursor **)(txn->mt_dbs + env->me_maxdbs);
 		if (parent) {
 			txn->mt_dbiseqs = parent->mt_dbiseqs;
@@ -2771,6 +2772,7 @@ mdb_txn_begin(MDB_env *env, MDB_txn *parent, unsigned int flags, MDB_txn **ret)
 			txn->mt_dbflags = (unsigned char *)(txn->mt_dbiseqs + env->me_maxdbs);
 		}
 	}
+	txn->mt_flags = flags;
 	txn->mt_env = env;
 
 ok:
@@ -2822,7 +2824,7 @@ ok:
 	} else {
 		*ret = txn;
 		DPRINTF(("begin txn %"Z"u%c %p on mdbenv %p, root page %"Z"u",
-			txn->mt_txnid, (txn->mt_flags & MDB_TXN_RDONLY) ? 'r' : 'w',
+			txn->mt_txnid, (flags & MDB_RDONLY) ? 'r' : 'w',
 			(void *) txn, (void *) env, txn->mt_dbs[MAIN_DBI].md_root));
 	}
 
@@ -3660,6 +3662,7 @@ mdb_env_write_meta(MDB_txn *txn)
 {
 	MDB_env *env;
 	MDB_meta	meta, metab, *mp;
+	unsigned flags;
 	size_t mapsize;
 	off_t off;
 	int rc, len, toggle;
@@ -3676,13 +3679,14 @@ mdb_env_write_meta(MDB_txn *txn)
 		toggle, txn->mt_dbs[MAIN_DBI].md_root));
 
 	env = txn->mt_env;
+	flags = txn->mt_flags & env->me_flags;
 	mp = env->me_metas[toggle];
 	mapsize = env->me_metas[toggle ^ 1]->mm_mapsize;
 	/* Persist any increases of mapsize config */
 	if (mapsize < env->me_mapsize)
 		mapsize = env->me_mapsize;
 
-	if (env->me_flags & MDB_WRITEMAP) {
+	if (flags & MDB_WRITEMAP) {
 		mp->mm_mapsize = mapsize;
 		mp->mm_dbs[0] = txn->mt_dbs[0];
 		mp->mm_dbs[1] = txn->mt_dbs[1];
@@ -3692,9 +3696,7 @@ mdb_env_write_meta(MDB_txn *txn)
 		__sync_synchronize();
 #endif
 		mp->mm_txnid = txn->mt_txnid;
-		if (txn->mt_flags & (MDB_TXN_NOSYNC|MDB_TXN_NOMETASYNC))
-			goto done;
-		if (!(env->me_flags & (MDB_NOMETASYNC|MDB_NOSYNC))) {
+		if (!(flags & (MDB_NOMETASYNC|MDB_NOSYNC))) {
 			unsigned meta_size = env->me_psize;
 			rc = (env->me_flags & MDB_MAPASYNC) ? MS_ASYNC : MS_SYNC;
 			ptr = env->me_map;
@@ -3730,9 +3732,7 @@ mdb_env_write_meta(MDB_txn *txn)
 	off += PAGEHDRSZ;
 
 	/* Write to the SYNC fd */
-	mfd = ((env->me_flags & (MDB_NOSYNC|MDB_NOMETASYNC)) ||
-		(txn->mt_flags & (MDB_TXN_NOSYNC|MDB_TXN_NOMETASYNC))) ?
-		env->me_fd : env->me_mfd;
+	mfd = (flags & (MDB_NOSYNC|MDB_NOMETASYNC)) ? env->me_fd : env->me_mfd;
 #ifdef _WIN32
 	{
 		memset(&ov, 0, sizeof(ov));
@@ -5133,7 +5133,7 @@ mdb_page_get(MDB_txn *txn, pgno_t pgno, MDB_page **ret, int *lvl)
 	MDB_page *p = NULL;
 	int level;
 
-	if (!((txn->mt_flags & MDB_TXN_RDONLY) | (env->me_flags & MDB_WRITEMAP))) {
+	if (! (txn->mt_flags & (MDB_TXN_RDONLY|MDB_TXN_WRITEMAP))) {
 		MDB_txn *tx2 = txn;
 		level = 1;
 		do {