diff --git a/libraries/liblmdb/lmdb.h b/libraries/liblmdb/lmdb.h
index ff82017..5f2216e 100644
--- a/libraries/liblmdb/lmdb.h
+++ b/libraries/liblmdb/lmdb.h
@@ -263,8 +263,6 @@ typedef int  (MDB_cmp_func)(const MDB_val *a, const MDB_val *b);
 typedef void (MDB_rel_func)(MDB_val *item, void *oldptr, void *newptr, void *relctx);
 
 /** @defgroup	mdb_env	Environment Flags
- *
- *	Values do not overlap Database Flags.
  *	@{
  */
 	/** mmap at a fixed address (experimental) */
@@ -292,8 +290,6 @@ typedef void (MDB_rel_func)(MDB_val *item, void *oldptr, void *newptr, void *rel
 /** @} */
 
 /**	@defgroup	mdb_dbi_open	Database Flags
- *
- *	Values do not overlap Environment Flags.
  *	@{
  */
 	/** use reverse string keys */
diff --git a/libraries/liblmdb/mdb.c b/libraries/liblmdb/mdb.c
index a8d0428..7860471 100644
--- a/libraries/liblmdb/mdb.c
+++ b/libraries/liblmdb/mdb.c
@@ -4011,6 +4011,10 @@ fail:
 #define	CHANGELESS	(MDB_FIXEDMAP|MDB_NOSUBDIR|MDB_RDONLY|MDB_WRITEMAP| \
 	MDB_NOTLS|MDB_NOLOCK|MDB_NORDAHEAD)
 
+#if VALID_FLAGS & PERSISTENT_FLAGS & (CHANGEABLE|CHANGELESS)
+# error "Persistent DB flags & env flags overlap, but both go in mm_flags"
+#endif
+
 int
 mdb_env_open(MDB_env *env, const char *path, unsigned int flags, mdb_mode_t mode)
 {