diff --git a/libraries/liblmdb/mdb.c b/libraries/liblmdb/mdb.c
index 16544d5..e3eef1c 100644
--- a/libraries/liblmdb/mdb.c
+++ b/libraries/liblmdb/mdb.c
@@ -2429,7 +2429,7 @@ mdb_page_alloc(MDB_cursor *mc, int num, MDB_page **mp)
 			goto fail;
 	}
 #ifdef _WIN32
-	if (env->me_flags & MDB_WRITEMAP) {
+	if (!(env->me_flags & MDB_RDONLY)) {
 		void *p;
 		p = (MDB_page *)(env->me_map + env->me_psize * pgno);
 		p = VirtualAlloc(p, env->me_psize * num, MEM_COMMIT,