diff --git a/src/include/storage/md.h b/src/include/storage/md.h
index 569a00336a6d2..03be8dc200168 100644
--- a/src/include/storage/md.h
+++ b/src/include/storage/md.h
@@ -24,7 +24,7 @@ extern PGDLLIMPORT PgAioHandleCallbacks aio_md_readv_cb;
 
 /* registration function for md storage manager */
 extern void mdsmgr_register(void);
-extern SMgrId MdSMgrId;
+extern PGDLLIMPORT SMgrId MdSMgrId;
 
 /* md storage manager functionality */
 extern void mdinit(void);