diff --git a/appl/kx/kx.h b/appl/kx/kx.h
index 20e0ff918..4f53fc966 100644
--- a/appl/kx/kx.h
+++ b/appl/kx/kx.h
@@ -112,7 +112,8 @@
 #include <sys/stropts.h>
 #endif
 
-#if defined(HAVE_SYS_STROPTS_H) && defined(HAVE_FATTACH) && defined(I_PUSH)
+/* as far as we know, this is only used with later versions of Slowlaris */
+#if SunOS == 5 && defined(HAVE_SYS_STROPTS_H) && defined(HAVE_FATTACH) && defined(I_PUSH)
 #define MAY_HAVE_X11_PIPES
 #endif