diff --git a/bootstrap.sh b/bootstrap.sh
index c591b11e2..5071d7e74 100755
--- a/bootstrap.sh
+++ b/bootstrap.sh
@@ -1,8 +1,5 @@
 #!/usr/bin/env bash
 
-set -eu
-set -o pipefail
-
 : '
 
 todo
@@ -11,17 +8,19 @@ todo
 - shrink icu data
 '
 
-MASON_VERSION="v0.17.0"
+MASON_VERSION="fde1d9f5"
 
 function setup_mason() {
     if [[ ! -d ./.mason ]]; then
-        git clone https://github.com/mapbox/mason.git ./.mason
-        (cd ./.mason && git checkout ${MASON_VERSION})
-    else
-        echo "Updating to latest mason"
-        (cd ./.mason && git fetch && git checkout ${MASON_VERSION} && git pull origin ${MASON_VERSION})
+        git clone https://github.com/mapbox/mason.git .mason || return
+    elif ! git -C .mason rev-parse -q --verify "$MASON_VERSION" >/dev/null; then
+        git -C .mason fetch --all || true # non-fatal
     fi
-    export PATH=$(pwd)/.mason:$PATH
+    git -C .mason checkout --detach "$MASON_VERSION" -- || return
+    case ":$PATH:" in
+        *":$PWD/.mason:"*) : already there ;;
+        *) export PATH="$PWD/.mason:$PATH" ;;
+    esac
     export CXX=${CXX:-clang++}
     export CC=${CC:-clang}
 }
@@ -45,7 +44,7 @@ function install() {
 }
 
 ICU_VERSION="57.1"
-BOOST_VERSION="1.65.1"
+BOOST_VERSION="1.73.0"
 
 function install_mason_deps() {
     install ccache 3.3.1
@@ -60,9 +59,6 @@ function install_mason_deps() {
     install proj 4.9.3 libproj
     install pixman 0.34.0 libpixman-1
     install cairo 1.14.8 libcairo
-    install protobuf 3.2.0
-    # technically protobuf is not a mapnik core dep, but installing
-    # here by default helps make mapnik-vector-tile builds easier
     install webp 0.6.0 libwebp
     install libgdal 2.1.3 libgdal
     install boost ${BOOST_VERSION}
@@ -133,22 +129,46 @@ function setup_runtime_settings() {
     echo "export PROJ_LIB=${MASON_LINKED_ABS}/share/proj" > mapnik-settings.env
     echo "export ICU_DATA=${MASON_LINKED_ABS}/share/icu/${ICU_VERSION}" >> mapnik-settings.env
     echo "export GDAL_DATA=${MASON_LINKED_ABS}/share/gdal" >> mapnik-settings.env
-    source mapnik-settings.env
+}
+
+# turn arguments of the form NAME=VALUE into exported variables;
+# any other arguments are reported and cause error return status
+function export_variables() {
+    local arg= ret=0
+    for arg
+    do
+        if [[ "$arg" =~ ^[[:alpha:]][_[:alnum:]]*= ]]
+        then
+            export "$arg"
+        else
+            printf >&2 "bootstrap.sh: invalid argument: %s\n" "$arg"
+            ret=1
+        fi
+    done
+    return $ret
 }
 
 function main() {
-    setup_mason
-    install_mason_deps
-    make_config > ./config.py
-    setup_runtime_settings
-    echo "Ready, now run:"
-    echo ""
-    echo "    ./configure && make"
+    export_variables "$@" || return
+    # setup_mason must not run in subshell, because it sets default
+    # values of CC, CXX and adds mason to PATH, which we want to keep
+    # when sourced
+    setup_mason || return
+    (
+        # this is wrapped in subshell to allow sourcing this script
+        # without having the terminal closed on error
+        set -eu
+        set -o pipefail
+
+        install_mason_deps
+        make_config > ./config.py
+        setup_runtime_settings
+
+        printf "\n\e[1;32m%s\e[m\n" "bootstrap successful, now run:"
+        echo ""
+        echo "    ./configure && make"
+        echo ""
+    )
 }
 
-main
-
-# allow sourcing of script without
-# causing the terminal to bail on error
-set +eu
-set +o pipefail
+main "$@"