http://git.savannah.gnu.org/cgit/gforth.git/commit/?id=4a03e4ff51314fc3a97acedeee928822b3bf1433

--- arch/mips/machine.h.orig	Fri Oct 11 23:31:28 2013
+++ arch/mips/machine.h	Tue Jan 26 09:04:42 2016
@@ -26,8 +26,10 @@
 #endif
 
 /* cache flush stuff */
-#ifdef ultrix
+#if defined(ultrix)
 #include <mips/cachectl.h>
+#elif defined(__OpenBSD__)
+#include <mips64/sysarch.h>
 #else
 /* works on Irix */
 #include <sys/cachectl.h>