diff --git a/libraries/liblmdb/mdb.c b/libraries/liblmdb/mdb.c
index 1edc282..73c80da 100644
--- a/libraries/liblmdb/mdb.c
+++ b/libraries/liblmdb/mdb.c
@@ -35,6 +35,9 @@
 #ifndef _GNU_SOURCE
 #define _GNU_SOURCE 1
 #endif
+#if defined(__WIN64__)
+#define _FILE_OFFSET_BITS	64
+#endif
 #ifdef _WIN32
 #include <malloc.h>
 #include <windows.h>