diff --git a/build.sh b/build.sh
index c7e3c0b..1a86b63 100755
--- a/build.sh
+++ b/build.sh
@@ -9,6 +9,8 @@ for __ in subr/*.subr; do . "${__}"; done;
 set -o noglob;
 while [ ${#} -gt 0 ]; do
 case ${1} in
+-4)	ARG_IPV4_ONLY=1; ;;
+-6)	ARG_IPV6_ONLY=1; ;;
 -c)	ARG_CLEAN=1; ;;
 -C)	ARG_CHECK_UPDATES=1; ;;
 -N)	ARG_OFFLINE=1; ;;
diff --git a/etc/build.usage b/etc/build.usage
index 4afb450..18be3f4 100644
--- a/etc/build.usage
+++ b/etc/build.usage
@@ -1,7 +1,9 @@
-usage: ./build.sh [-x] [-a nt32|nt64] [-b debug|release] [-c] [-C] [-h]
-                  [-i] [-N] [-r package[,...][:step]] [-R] [-t[.gz|.bz2|.xz]
+usage: ./build.sh [-x] [-4] [-6] [-a nt32|nt64] [-b debug|release] [-c] [-C]
+                  [-h] [-i] [-N] [-r package[,...][:step]] [-R] [-t[.gz|.bz2|.xz]
                   [-v] [<target>[ ...]]
         -x                      Set the xtrace sh(1)ell option for debugging purposes.
+        -4                      Force IPv4 when downloading files.
+        -6                      Force IPv6 when downloading files.
         -a nt32|nt64            Selects 32-bit or 64-bit architecture; defaults to nt64.
         -b debug|release        Selects debug or release build; defaults to debug.
                                 This currently only controls CFLAGS.
diff --git a/subr/pre_setup_env.subr b/subr/pre_setup_env.subr
index b8e1faa..d5de277 100644
--- a/subr/pre_setup_env.subr
+++ b/subr/pre_setup_env.subr
@@ -11,6 +11,11 @@ pre_setup_env() {
 	for __ in ${HOME}/midipix_build.vars ../midipix_build.vars ./vars/build.vars; do
 		[ -e ${__} ] && . ${__};
 	done;
+	if [ ${ARG_IPV4_ONLY:-0} -eq 1 ]; then
+		WGET_ARGS="-4${WGET_ARGS:+ ${WGET_ARGS}}";
+	elif [ ${ARG_IPV6_ONLY:-0} -eq 1 ]; then
+		WGET_ARGS="-6${WGET_ARGS:+ ${WGET_ARGS}}";
+	fi;
 	for __ in $(export | sed -e 's/^export //' -e 's/=.*$//'); do
 		if ! lmatch "${CLEAR_ENV_VARS_EXCEPT}" " " "${__}"; then
 			unset "${__}";