diff --git a/src/proto/os_win32.pro b/src/proto/os_win32.pro
index 1431f69..5816fc9 100644
--- a/src/proto/os_win32.pro
+++ b/src/proto/os_win32.pro
@@ -43,6 +43,7 @@
 void mch_delay __ARGS((long msec, int ignoreinput));
 int mch_remove __ARGS((char_u *name));
 void mch_breakcheck __ARGS((void));
+long_u mch_total_mem __ARGS((int special));
 int mch_wrename __ARGS((WCHAR *wold, WCHAR *wnew));
 int mch_rename __ARGS((const char *pszOldFile, const char *pszNewFile));
 char *default_shell __ARGS((void));