diff --git a/Makefile b/Makefile
index 26dfcb45a..b3a8e7acd 100644
--- a/Makefile
+++ b/Makefile
@@ -382,7 +382,7 @@ endif
 ifeq ($(TARGET),aix51)
   set_target_defaults = $(call default_opts, \
     USE_POLL USE_LIBCRYPT USE_OBSOLETE_LINKER)
-  TARGET_CFLAGS   = -Dss_family=__ss_family
+  TARGET_CFLAGS   = -Dss_family=__ss_family -Dip6_hdr=ip6hdr -DSTEVENS_API
   DEBUG_CFLAGS    =
 endif