diff --git a/bochs/config.h.in b/bochs/config.h.in
index a821f691b..22c76d44b 100644
--- a/bochs/config.h.in
+++ b/bochs/config.h.in
@@ -186,12 +186,20 @@
 #define BX_USE_NEW_PIT 0
 
 #define BX_USE_SLOWDOWN_TIMER 0
-#define BX_USE_IDLE_HACK 0
 #define BX_HAVE_SLEEP 0
 #define BX_HAVE_USLEEP 0
 #define BX_HAVE_NANOSLEEP 0
 #define BX_HAVE_ABORT 0
 
+// This turns on Roland Mainz's idle hack.  Presently it is specific to 
+// X windows.  If people try to enable it elsewhere, give a compile error
+// so that they don't waste their time trying.
+#define BX_USE_IDLE_HACK 0
+#if (BX_USE_IDLE_HACK && !BX_WITH_X11)
+#  error IDLE_HACK will only work with the X11 gui. Correct configure args and retry.
+#endif
+
+
 // Use Static Member Funtions to eliminate 'this' pointer passing
 // If you want the efficiency of 'C', you can make all the
 // members of the C++ CPU class to be static.