diff --git a/src/macros.h b/src/macros.h
index d75d190..c320a3f 100644
--- a/src/macros.h
+++ b/src/macros.h
@@ -191,9 +191,6 @@
 # ifndef WIN32
 #   define mch_access(n, p)	access((n), (p))
 # endif
-# if !(defined(FEAT_MBYTE) && defined(WIN3264))
-#  define mch_fopen(n, p)	fopen((n), (p))
-# endif
 # define mch_fstat(n, p)	fstat((n), (p))
 # ifdef MSWIN	/* has it's own mch_stat() function */
 #  define mch_stat(n, p)	vim_stat((n), (p))
@@ -223,10 +220,6 @@
  * but it is not recommended, because it can destroy indexes etc.
  */
 #  define mch_open(n, m, p)	open(vms_fixfilename(n), (m), (p))
-# else
-#  if !(defined(FEAT_MBYTE) && defined(WIN3264))
-#   define mch_open(n, m, p)	open((n), (m), (p))
-#  endif
 # endif
 #endif
 
diff --git a/src/os_win32.c b/src/os_win32.c
index 8a38bcc..4921b50 100644
--- a/src/os_win32.c
+++ b/src/os_win32.c
@@ -6503,7 +6503,7 @@
  * Version of open() that may use UTF-16 file name.
  */
     int
-mch_open(char *name, int flags, int mode)
+mch_open(const char *name, int flags, int mode)
 {
     /* _wopen() does not work with Borland C 5.5: creates a read-only file. */
 # ifndef __BORLANDC__
@@ -6536,7 +6536,7 @@
  * Version of fopen() that may use UTF-16 file name.
  */
     FILE *
-mch_fopen(char *name, char *mode)
+mch_fopen(const char *name, const char *mode)
 {
     WCHAR	*wn, *wm;
     FILE	*f = NULL;
diff --git a/src/proto/os_win32.pro b/src/proto/os_win32.pro
index 6c5dc4f..754df4f 100644
--- a/src/proto/os_win32.pro
+++ b/src/proto/os_win32.pro
@@ -4,6 +4,8 @@
 void *get_dll_import_func(HINSTANCE hInst, const char *funcname);
 int dyn_libintl_init(void);
 void dyn_libintl_end(void);
+int null_libintl_putenv(const char *envstring);
+int null_libintl_wputenv(const wchar_t *envstring);
 void PlatformId(void);
 void mch_setmouse(int on);
 void mch_update_cursor(void);
@@ -56,8 +58,8 @@
 int mch_rename(const char *pszOldFile, const char *pszNewFile);
 char *default_shell(void);
 int mch_access(char *n, int p);
-int mch_open(char *name, int flags, int mode);
-FILE *mch_fopen(char *name, char *mode);
+int mch_open(const char *name, int flags, int mode);
+FILE *mch_fopen(const char *name, const char *mode);
 int mch_copy_file_attribute(char_u *from, char_u *to);
 int myresetstkoflw(void);
 int get_cmd_argsW(char ***argvp);
diff --git a/src/version.c b/src/version.c
index 1922837..d4a334d 100644
--- a/src/version.c
+++ b/src/version.c
@@ -770,6 +770,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    840,
+/**/
     839,
 /**/
     838,
diff --git a/src/vim.h b/src/vim.h
index 8b6337e..2562d9e 100644
--- a/src/vim.h
+++ b/src/vim.h
@@ -2141,6 +2141,11 @@
 # define number_width(x) 7
 #endif
 
+/* This must come after including proto.h */
+#if !(defined(FEAT_MBYTE) && defined(WIN3264))
+# define mch_open(n, m, p)	open((n), (m), (p))
+# define mch_fopen(n, p)	fopen((n), (p))
+#endif
 
 #include "globals.h"	    /* global variables and messages */