diff --git a/src/os_win16.h b/src/os_win16.h
index 17f876c..98f0ece 100644
--- a/src/os_win16.h
+++ b/src/os_win16.h
@@ -63,16 +63,21 @@
 
 #include <stdlib.h>
 #include <time.h>
-#include <dos.h>
-#include <dir.h>
 
-#ifndef STRICT
-# define STRICT
-#endif
-#ifndef COBJMACROS
-# define COBJMACROS	/* For OLE: Enable "friendlier" access to objects */
-#endif
-#include <windows.h>
+/* cproto fails on missing include files */
+#ifndef PROTO
+# include <dos.h>
+# include <dir.h>
+
+# ifndef STRICT
+#  define STRICT
+# endif
+# ifndef COBJMACROS
+#  define COBJMACROS	/* For OLE: Enable "friendlier" access to objects */
+# endif
+# include <windows.h>
+
+#endif /* PROTO */
 
 /*
  *  plenty of memory, use large buffers