diff --git a/Socket6.xs b/Socket6.xs
index 05c791c..058e9d9 100644
--- a/Socket6.xs
+++ b/Socket6.xs
@@ -105,10 +105,6 @@ const struct in6_addr in6addr_loopback = IN6ADDR_LOOPBACK_INIT;
 #define	HAVE_INET_PTON		1
 #endif
 
-#ifndef HAVE_PL_SV_UNDEF
-#define	PL_sv_undef		sv_undef
-#endif
-
 static int
 not_here(char *s)
 {
-- 
2.16.3