diff --git a/src/s/hpux9.h b/src/s/hpux9.h
index cc5f4e6c345..c622a392b05 100644
--- a/src/s/hpux9.h
+++ b/src/s/hpux9.h
@@ -46,3 +46,6 @@
 
 /* HP-UX doesn't supply nor need Xmu.  */
 #define LIBXMU
+
+/* zoo@armadillo.com says we don't need -lXext in HPUX 9.  */
+#undef LIBX11_SYSTEM