diff --git a/sys/arch/amd64/conf/Makefile.amd64 b/sys/arch/amd64/conf/Makefile.amd64
index c1455c1..8717926 100644
--- a/sys/arch/amd64/conf/Makefile.amd64
+++ b/sys/arch/amd64/conf/Makefile.amd64
@@ -43,6 +43,18 @@ CFLAGS+=	-msoft-float
 # For gcc we might need this, but other compilers barf
 # CFLAGS+=	-mno-fp-ret-in-387
 
+# By default, our gcc uses -mtune=nocona for compiling the kernels
+# (see share/mk/bsd.own.mk). With -mtune=nocona, gcc doesn't align
+# the start address of functions, i.e., they can move easily by changes
+# of leading functions, which causes performance fluctuations.
+# -falign-functions=16 reduces such fluctuations by supressing
+# changing of the start address of functions.
+DEFCOPTS.gcc?=	-falign-functions=16
+DEFCOPTS+=	${DEFCOPTS.${ACTIVE_CC}}
+.if "${COPTS}" != ""
+COPTS+=		${DEFCOPTS.${ACTIVE_CC}}
+.endif
+
 ##
 ## (3) libkern and compat
 ##