diff --git a/libraries/liblmdb/mdb.c b/libraries/liblmdb/mdb.c
index 613df45..2a3fb1a 100644
--- a/libraries/liblmdb/mdb.c
+++ b/libraries/liblmdb/mdb.c
@@ -1037,6 +1037,7 @@ struct MDB_txn {
 #define DB_STALE	0x02		/**< Named-DB record is older than txnID */
 #define DB_NEW		0x04		/**< Named-DB handle opened in this txn */
 #define DB_VALID	0x08		/**< DB handle is valid, see also #MDB_VALID */
+#define DB_USRVALID	0x10		/**< As #DB_VALID, but not set for #FREE_DBI */
 /** @} */
 	/** In write txns, array of cursors for each DB */
 	MDB_cursor	**mt_cursors;
@@ -1227,8 +1228,8 @@ typedef struct MDB_ntxn {
 #define MAX_WRITE		(0x80000000U >> (sizeof(ssize_t) == 4))
 
 	/** Check \b txn and \b dbi arguments to a function */
-#define TXN_DBI_EXIST(txn, dbi) \
-	((txn) && (dbi) < (txn)->mt_numdbs && ((txn)->mt_dbflags[dbi] & DB_VALID))
+#define TXN_DBI_EXIST(txn, dbi, validity) \
+	((txn) && (dbi)<(txn)->mt_numdbs && ((txn)->mt_dbflags[dbi] & (validity)))
 
 	/** Check for misused \b dbi handles */
 #define TXN_DBI_CHANGED(txn, dbi) \
@@ -2662,9 +2663,10 @@ mdb_txn_renew0(MDB_txn *txn)
 	for (i=2; i<txn->mt_numdbs; i++) {
 		x = env->me_dbflags[i];
 		txn->mt_dbs[i].md_flags = x & PERSISTENT_FLAGS;
-		txn->mt_dbflags[i] = (x & MDB_VALID) ? DB_VALID|DB_STALE : 0;
+		txn->mt_dbflags[i] = (x & MDB_VALID) ? DB_VALID|DB_USRVALID|DB_STALE : 0;
 	}
-	txn->mt_dbflags[0] = txn->mt_dbflags[1] = DB_VALID;
+	txn->mt_dbflags[MAIN_DBI] = DB_VALID|DB_USRVALID;
+	txn->mt_dbflags[FREE_DBI] = DB_VALID;
 
 	if (env->me_maxpg < txn->mt_next_pgno) {
 		mdb_txn_reset0(txn, "renew0-mapfail");
@@ -5466,7 +5468,7 @@ mdb_get(MDB_txn *txn, MDB_dbi dbi,
 
 	DPRINTF(("===> get db %u key [%s]", dbi, DKEY(key)));
 
-	if (!key || !data || dbi == FREE_DBI || !TXN_DBI_EXIST(txn, dbi))
+	if (!key || !data || !TXN_DBI_EXIST(txn, dbi, DB_USRVALID))
 		return EINVAL;
 
 	if (txn->mt_flags & MDB_TXN_ERROR)
@@ -7207,7 +7209,7 @@ mdb_xcursor_init1(MDB_cursor *mc, MDB_node *node)
 	}
 	DPRINTF(("Sub-db -%u root page %"Z"u", mx->mx_cursor.mc_dbi,
 		mx->mx_db.md_root));
-	mx->mx_dbflag = DB_VALID|DB_DIRTY; /* DB_DIRTY guides mdb_cursor_touch */
+	mx->mx_dbflag = DB_VALID|DB_USRVALID|DB_DIRTY; /* DB_DIRTY guides mdb_cursor_touch */
 #if UINT_MAX < SIZE_MAX
 	if (mx->mx_dbx.md_cmp == mdb_cmp_int && mx->mx_db.md_pad == sizeof(size_t))
 		mx->mx_dbx.md_cmp = mdb_cmp_clong;
@@ -7280,7 +7282,7 @@ mdb_cursor_open(MDB_txn *txn, MDB_dbi dbi, MDB_cursor **ret)
 	MDB_cursor	*mc;
 	size_t size = sizeof(MDB_cursor);
 
-	if (!ret || !TXN_DBI_EXIST(txn, dbi))
+	if (!ret || !TXN_DBI_EXIST(txn, dbi, DB_VALID))
 		return EINVAL;
 
 	if (txn->mt_flags & MDB_TXN_ERROR)
@@ -7312,7 +7314,7 @@ mdb_cursor_open(MDB_txn *txn, MDB_dbi dbi, MDB_cursor **ret)
 int
 mdb_cursor_renew(MDB_txn *txn, MDB_cursor *mc)
 {
-	if (!mc || !TXN_DBI_EXIST(txn, mc->mc_dbi))
+	if (!mc || !TXN_DBI_EXIST(txn, mc->mc_dbi, DB_VALID))
 		return EINVAL;
 
 	if ((mc->mc_flags & C_UNTRACK) || txn->mt_cursors)
@@ -8084,7 +8086,7 @@ int
 mdb_del(MDB_txn *txn, MDB_dbi dbi,
     MDB_val *key, MDB_val *data)
 {
-	if (!key || dbi == FREE_DBI || !TXN_DBI_EXIST(txn, dbi))
+	if (!key || !TXN_DBI_EXIST(txn, dbi, DB_USRVALID))
 		return EINVAL;
 
 	if (txn->mt_flags & (MDB_TXN_RDONLY|MDB_TXN_ERROR))
@@ -8550,7 +8552,7 @@ mdb_put(MDB_txn *txn, MDB_dbi dbi,
 	MDB_cursor mc;
 	MDB_xcursor mx;
 
-	if (!key || !data || dbi == FREE_DBI || !TXN_DBI_EXIST(txn, dbi))
+	if (!key || !data || !TXN_DBI_EXIST(txn, dbi, DB_USRVALID))
 		return EINVAL;
 
 	if (flags & ~(MDB_NOOVERWRITE|MDB_NODUPDATA|MDB_RESERVE|MDB_APPEND|MDB_APPENDDUP))
@@ -9320,7 +9322,7 @@ int mdb_dbi_open(MDB_txn *txn, const char *name, unsigned int flags, MDB_dbi *db
 		return (flags & MDB_CREATE) ? MDB_INCOMPATIBLE : MDB_NOTFOUND;
 
 	/* Find the DB info */
-	dbflag = DB_NEW|DB_VALID;
+	dbflag = DB_NEW|DB_VALID|DB_USRVALID;
 	exact = 0;
 	key.mv_size = len;
 	key.mv_data = (void *)name;
@@ -9368,7 +9370,7 @@ int mdb_dbi_open(MDB_txn *txn, const char *name, unsigned int flags, MDB_dbi *db
 
 int mdb_stat(MDB_txn *txn, MDB_dbi dbi, MDB_stat *arg)
 {
-	if (!arg || !TXN_DBI_EXIST(txn, dbi))
+	if (!arg || !TXN_DBI_EXIST(txn, dbi, DB_VALID))
 		return EINVAL;
 
 	if (txn->mt_flags & MDB_TXN_ERROR)
@@ -9402,7 +9404,7 @@ void mdb_dbi_close(MDB_env *env, MDB_dbi dbi)
 int mdb_dbi_flags(MDB_txn *txn, MDB_dbi dbi, unsigned int *flags)
 {
 	/* We could return the flags for the FREE_DBI too but what's the point? */
-	if (dbi == FREE_DBI || !TXN_DBI_EXIST(txn, dbi))
+	if (!TXN_DBI_EXIST(txn, dbi, DB_USRVALID))
 		return EINVAL;
 	*flags = txn->mt_dbs[dbi].md_flags & PERSISTENT_FLAGS;
 	return MDB_SUCCESS;
@@ -9502,7 +9504,7 @@ int mdb_drop(MDB_txn *txn, MDB_dbi dbi, int del)
 	MDB_cursor *mc, *m2;
 	int rc;
 
-	if ((unsigned)del > 1 || dbi == FREE_DBI || !TXN_DBI_EXIST(txn, dbi))
+	if ((unsigned)del > 1 || !TXN_DBI_EXIST(txn, dbi, DB_USRVALID))
 		return EINVAL;
 
 	if (F_ISSET(txn->mt_flags, MDB_TXN_RDONLY))
@@ -9550,7 +9552,7 @@ leave:
 
 int mdb_set_compare(MDB_txn *txn, MDB_dbi dbi, MDB_cmp_func *cmp)
 {
-	if (dbi == FREE_DBI || !TXN_DBI_EXIST(txn, dbi))
+	if (!TXN_DBI_EXIST(txn, dbi, DB_USRVALID))
 		return EINVAL;
 
 	txn->mt_dbxs[dbi].md_cmp = cmp;
@@ -9559,7 +9561,7 @@ int mdb_set_compare(MDB_txn *txn, MDB_dbi dbi, MDB_cmp_func *cmp)
 
 int mdb_set_dupsort(MDB_txn *txn, MDB_dbi dbi, MDB_cmp_func *cmp)
 {
-	if (dbi == FREE_DBI || !TXN_DBI_EXIST(txn, dbi))
+	if (!TXN_DBI_EXIST(txn, dbi, DB_USRVALID))
 		return EINVAL;
 
 	txn->mt_dbxs[dbi].md_dcmp = cmp;
@@ -9568,7 +9570,7 @@ int mdb_set_dupsort(MDB_txn *txn, MDB_dbi dbi, MDB_cmp_func *cmp)
 
 int mdb_set_relfunc(MDB_txn *txn, MDB_dbi dbi, MDB_rel_func *rel)
 {
-	if (dbi == FREE_DBI || !TXN_DBI_EXIST(txn, dbi))
+	if (!TXN_DBI_EXIST(txn, dbi, DB_USRVALID))
 		return EINVAL;
 
 	txn->mt_dbxs[dbi].md_rel = rel;
@@ -9577,7 +9579,7 @@ int mdb_set_relfunc(MDB_txn *txn, MDB_dbi dbi, MDB_rel_func *rel)
 
 int mdb_set_relctx(MDB_txn *txn, MDB_dbi dbi, void *ctx)
 {
-	if (dbi == FREE_DBI || !TXN_DBI_EXIST(txn, dbi))
+	if (!TXN_DBI_EXIST(txn, dbi, DB_USRVALID))
 		return EINVAL;
 
 	txn->mt_dbxs[dbi].md_relctx = ctx;