Index: net-mgmt/fastnetmon/Makefile
===================================================================
--- net-mgmt/fastnetmon/Makefile
+++ net-mgmt/fastnetmon/Makefile
@@ -30,6 +30,12 @@
 
 PORTDOCS=	*
 
+.include <bsd.port.pre.mk>
+
+.if ${ARCH} == "i386" && empty(MACHINE_CPU:Mi586)
+CFLAGS+=	-march=i586
+.endif
+
 post-patch:
 	@${REINPLACE_CMD} -e 's|/usr/local|${LOCALBASE}|' ${WRKSRC}/src/CMakeLists.txt
 	@${REINPLACE_CMD} -e 's|/usr/local|${PREFIX}|; \
@@ -43,4 +49,4 @@
 	cd ${WRKSRC} && ${COPYTREE_SHARE} "README.md docs" ${STAGEDIR}${DOCSDIR}
 	${MKDIR} ${STAGEDIR}/var/run/fastnetmon ${STAGEDIR}/var/log/fastnetmon
 
-.include <bsd.port.mk>
+.include <bsd.port.post.mk>