diff --git a/lib/libmilter/Makefile b/lib/libmilter/Makefile
index d75fcd41865f..3e89e332454c 100644
--- a/lib/libmilter/Makefile
+++ b/lib/libmilter/Makefile
@@ -4,9 +4,13 @@ SENDMAIL_DIR=${.CURDIR}/../../contrib/sendmail
 .PATH:	${SENDMAIL_DIR}/libmilter ${SENDMAIL_DIR}/libsm
 
 CFLAGS+=-I${SENDMAIL_DIR}/src -I${SENDMAIL_DIR}/include -I.
-CFLAGS+=-DNETINET6 -DNOT_SENDMAIL -Dsm_snprintf=snprintf
+CFLAGS+=-DNOT_SENDMAIL -Dsm_snprintf=snprintf
 CFLAGS+=-D_THREAD_SAFE
 
+.if !defined(NOINET6)
+CFLAGS+=-DNETINET6
+.endif
+
 # User customizations to the sendmail build environment
 CFLAGS+=${SENDMAIL_CFLAGS}
 
diff --git a/lib/libsm/Makefile b/lib/libsm/Makefile
index c8ec07bd893f..56e5ac3d482c 100644
--- a/lib/libsm/Makefile
+++ b/lib/libsm/Makefile
@@ -4,7 +4,11 @@ SENDMAIL_DIR=${.CURDIR}/../../contrib/sendmail
 .PATH:	${SENDMAIL_DIR}/libsm
 
 CFLAGS+=-I${SENDMAIL_DIR}/src -I${SENDMAIL_DIR}/include -I.
-CFLAGS+=-DNETINET6 -DNEWDB -DNIS -DMAP_REGEX -DNOT_SENDMAIL
+CFLAGS+=-DNEWDB -DNIS -DMAP_REGEX -DNOT_SENDMAIL
+
+.if !defined(NOINET6)
+CFLAGS+=-DNETINET6
+.endif
 
 # User customizations to the sendmail build environment
 CFLAGS+=${SENDMAIL_CFLAGS}
diff --git a/usr.sbin/sendmail/Makefile b/usr.sbin/sendmail/Makefile
index 26b20829cd49..c1c838186c46 100644
--- a/usr.sbin/sendmail/Makefile
+++ b/usr.sbin/sendmail/Makefile
@@ -32,7 +32,11 @@ MAPS=	-DMAP_REGEX -DDNSMAP
 
 CSTD?=	c89
 CFLAGS+= -I${SMDIR} -I${SENDMAIL_DIR}/include -I.
-CFLAGS+= ${DBMDEF} ${NIS} -DMILTER -DNETINET6 -DTCPWRAPPERS ${MAPS}
+CFLAGS+= ${DBMDEF} ${NIS} -DMILTER -DTCPWRAPPERS ${MAPS}
+
+.if !defined(NOINET6)
+CFLAGS+= -DNETINET6
+.endif
 
 DPADD=	${LIBUTIL} ${LIBWRAP}
 LDADD=	-lutil -lwrap