diff --git a/libraries/libmdb/mdb.c b/libraries/libmdb/mdb.c
index 92362a3..091e8ec 100644
--- a/libraries/libmdb/mdb.c
+++ b/libraries/libmdb/mdb.c
@@ -6707,6 +6707,9 @@ mdb_default_cmp(MDB_txn *txn, MDB_dbi dbi)
 		 : ((f & MDB_REVERSEDUP) ? mdb_cmp_memnr : mdb_cmp_memn));
 }
 
+#define PERSISTENT_FLAGS	0xffff
+#define VALID_FLAGS	(MDB_REVERSEKEY|MDB_DUPSORT|MDB_INTEGERKEY|MDB_DUPFIXED|\
+	MDB_INTEGERDUP|MDB_REVERSEDUP|MDB_CREATE)
 int mdb_open(MDB_txn *txn, const char *name, unsigned int flags, MDB_dbi *dbi)
 {
 	MDB_val key, data;
@@ -6720,13 +6723,17 @@ int mdb_open(MDB_txn *txn, const char *name, unsigned int flags, MDB_dbi *dbi)
 		mdb_default_cmp(txn, FREE_DBI);
 	}
 
+	if ((flags & VALID_FLAGS) != flags)
+		return EINVAL;
+
 	/* main DB? */
 	if (!name) {
 		*dbi = MAIN_DBI;
-		if (flags & (MDB_DUPSORT|MDB_REVERSEKEY|MDB_INTEGERKEY)) {
+		if (flags & PERSISTENT_FLAGS) {
+			uint16_t f2 = flags & PERSISTENT_FLAGS;
 			/* make sure flag changes get committed */
-			if ((txn->mt_dbs[MAIN_DBI].md_flags | flags) != txn->mt_dbs[MAIN_DBI].md_flags) {
-				txn->mt_dbs[MAIN_DBI].md_flags |= (flags & (MDB_DUPSORT|MDB_REVERSEKEY|MDB_INTEGERKEY));
+			if ((txn->mt_dbs[MAIN_DBI].md_flags | f2) != txn->mt_dbs[MAIN_DBI].md_flags) {
+				txn->mt_dbs[MAIN_DBI].md_flags |= f2;
 				txn->mt_flags |= MDB_TXN_DIRTY;
 			}
 		}
@@ -6776,7 +6783,7 @@ int mdb_open(MDB_txn *txn, const char *name, unsigned int flags, MDB_dbi *dbi)
 		data.mv_data = &dummy;
 		memset(&dummy, 0, sizeof(dummy));
 		dummy.md_root = P_INVALID;
-		dummy.md_flags = flags & 0xffff;
+		dummy.md_flags = flags & PERSISTENT_FLAGS;
 		rc = mdb_cursor_put(&mc, &key, &data, F_SUBDATA);
 		dbflag = DB_DIRTY;
 	}