diff --git a/mk-sbuild b/mk-sbuild
index df2e9e5..56a5646 100755
--- a/mk-sbuild
+++ b/mk-sbuild
@@ -459,6 +459,8 @@ if [ -n "$DEBOOTSTRAP_EXCLUDE" ] ; then
 fi
 
 # if http_proxy is set in the environment (even empty) set 'proxy' to it
+[ "$proxy" = "_unset_" -a "${DEBOOTSTRAP_PROXY-xx}" = "xx" ] &&
+    proxy=${DEBOOTSTRAP_PROXY}
 [ "$proxy" = "_unset_" -a "${http_proxy-xx}" = "xx" ] && proxy=${http_proxy}
 if [ "$proxy" = "_unset_" ]; then
    _out=$(apt-config shell x Acquire::HTTP::Proxy) &&