diff --git a/src/proto/os_win32.pro b/src/proto/os_win32.pro
index dac2b71..b3c85b7 100644
--- a/src/proto/os_win32.pro
+++ b/src/proto/os_win32.pro
@@ -1,5 +1,5 @@
 /* os_win32.c */
-HINSTANCE vimLoadLib(char *name);
+HINSTANCE vimLoadLib(const char *name);
 int mch_is_gui_executable(void);
 HINSTANCE find_imported_module_by_funcname(HINSTANCE hInst, const char *funcname);
 void *get_dll_import_func(HINSTANCE hInst, const char *funcname);