diff --git a/vpnor/test/write_prsv.cpp b/vpnor/test/write_prsv.cpp
index f880476..b89b954 100644
--- a/vpnor/test/write_prsv.cpp
+++ b/vpnor/test/write_prsv.cpp
@@ -10,7 +10,9 @@
 
 #include "common.h"
 #include "mbox.h"
+extern "C" {
 #include "flash.h"
+}
 
 #include "vpnor/test/tmpd.hpp"