--- Libc/Libc-391.2.3/Makefile
+++ Libc/Libc-391.4.2/Makefile
@@ -25,6 +25,9 @@
 CFLAGS += -D__DARWIN_UNIX03=1
 .else
 CFLAGS += -D__DARWIN_UNIX03=0
+.endif
+.if (${MACHINE_ARCH} == i386)
+CFLAGS += -march=prescott -msse3
 .endif
 CFLAGS += -D__LIBC__ -DNOID -I${.CURDIR}/include
 .ifdef ALTLIBCHEADERS