diff --git a/lib/libmd/Makefile b/lib/libmd/Makefile
index 9559761aa002..a91fd057c689 100644
--- a/lib/libmd/Makefile
+++ b/lib/libmd/Makefile
@@ -97,7 +97,7 @@ CFLAGS+= -I${.CURDIR} -I${SRCTOP}/sys/crypto/sha2
 CFLAGS+= -I${SRCTOP}/sys/crypto/skein
 CFLAGS+= -DWEAK_REFS
 # unroll the 256 and 512 loops, half unroll the 1024
-CFLAGS+= -DSKEIN_LOOP=995
+CFLAGS.skein_block.c+= -DSKEIN_LOOP=995
 .PATH: ${.CURDIR}/${MACHINE_ARCH} ${SRCTOP}/sys/crypto/sha2
 .PATH: ${SRCTOP}/sys/crypto/skein ${SRCTOP}/sys/crypto/skein/${MACHINE_ARCH}
 
diff --git a/sys/modules/crypto/Makefile b/sys/modules/crypto/Makefile
index 952501ffce06..5d4509dedf01 100644
--- a/sys/modules/crypto/Makefile
+++ b/sys/modules/crypto/Makefile
@@ -27,7 +27,7 @@ SRCS	+= des_ecb.c des_enc.c des_setkey.c
 SRCS	+= sha1.c sha256c.c sha512c.c
 SRCS	+= skein.c skein_block.c
 # unroll the 256 and 512 loops, half unroll the 1024
-CFLAGS+= -DSKEIN_LOOP=995
+CFLAGS.skein_block.c	+= -DSKEIN_LOOP=995
 .if exists(${MACHINE_ARCH}/skein_block_asm.s)
 .PATH:	${SRCTOP}/sys/crypto/skein/${MACHINE_ARCH}
 SRCS	+= skein_block_asm.s