diff --git a/src/os_win32.c b/src/os_win32.c
index 96e115c..f5e283e 100644
--- a/src/os_win32.c
+++ b/src/os_win32.c
@@ -29,7 +29,11 @@
 #include <sys/types.h>
 #include <signal.h>
 #include <limits.h>
-#include <process.h>
+
+/* cproto fails on missing include files */
+#ifndef PROTO
+# include <process.h>
+#endif
 
 #undef chdir
 #ifdef __GNUC__
@@ -40,8 +44,10 @@
 # include <direct.h>
 #endif
 
-#if defined(FEAT_TITLE) && !defined(FEAT_GUI_W32)
-# include <shellapi.h>
+#ifndef PROTO
+# if defined(FEAT_TITLE) && !defined(FEAT_GUI_W32)
+#  include <shellapi.h>
+# endif
 #endif
 
 #ifdef __MINGW32__
@@ -125,6 +131,7 @@
 typedef int WORD;
 typedef int WCHAR;
 typedef void VOID;
+typedef int BY_HANDLE_FILE_INFORMATION;
 #endif
 
 #ifndef FEAT_GUI_W32
@@ -152,6 +159,8 @@
 # define wcsicmp(a, b) wcscmpi((a), (b))
 #endif
 
+#ifndef PROTO
+
 /* Enable common dialogs input unicode from IME if posible. */
 #ifdef FEAT_MBYTE
 LRESULT (WINAPI *pDispatchMessage)(LPMSG) = DispatchMessage;
@@ -160,6 +169,8 @@
 BOOL (WINAPI *pPeekMessage)(LPMSG, HWND, UINT, UINT, UINT) = PeekMessage;
 #endif
 
+#endif /* PROTO */
+
 #ifndef FEAT_GUI_W32
 /* Win32 Console handles for input and output */
 static HANDLE g_hConIn  = INVALID_HANDLE_VALUE;
@@ -453,7 +464,10 @@
 DWORD g_PlatformId;
 
 #ifdef HAVE_ACL
-# include <aclapi.h>
+# ifndef PROTO
+#  include <aclapi.h>
+# endif
+
 /*
  * These are needed to dynamically load the ADVAPI DLL, which is not
  * implemented under Windows 95 (and causes VIM to crash)
@@ -1658,8 +1672,10 @@
 #endif /* FEAT_GUI_W32 */
 }
 
-#ifndef __MINGW32__
-# include <shellapi.h>	/* required for FindExecutable() */
+#ifndef PROTO
+# ifndef __MINGW32__
+#  include <shellapi.h>	/* required for FindExecutable() */
+# endif
 #endif
 
 /*