diff --git a/src/makefiles/Makefile.irix5 b/src/makefiles/Makefile.irix5
index 0aa79e28c9..7cdf43cbe1 100644
--- a/src/makefiles/Makefile.irix5
+++ b/src/makefiles/Makefile.irix5
@@ -6,4 +6,5 @@ MK_NO_LORDER= true
 %.so: %.o
 	$(LD) -G -Bdynamic -shared -o $@ $< 
 
+CFLAGS+= -U_NO_XOPEN4