diff --git a/Makefile b/Makefile
index ea1bfe3..0686c47 100644
--- a/Makefile
+++ b/Makefile
@@ -2,6 +2,8 @@ dev_build_version=$(shell git describe --tags --always --dirty)
 
 export PATH := $(shell pwd)/.tmp/protoc/bin:$(PATH)
 
+export PROTOC_VERSION := 22.0
+
 # TODO: run golint and errcheck, but only to catch *new* violations and
 # decide whether to change code or not (e.g. we need to be able to whitelist
 # violations already in the code). They can be useful to catch errors, but
@@ -88,6 +90,6 @@ errcheck:
 test:
 	go test -race ./...
 
-.tmp/protoc/bin/protoc:
+.tmp/protoc/bin/protoc: ./Makefile ./download_protoc.sh
 	./download_protoc.sh
 
diff --git a/download_protoc.sh b/download_protoc.sh
index 5190003..6bbd135 100755
--- a/download_protoc.sh
+++ b/download_protoc.sh
@@ -4,7 +4,10 @@ set -e
 
 cd $(dirname $0)
 
-PROTOC_VERSION="22.0"
+if [[ -z "$PROTOC_VERSION" ]]; then
+  echo "Set PROTOC_VERSION env var to indicate the version to download" >&2
+  exit 1
+fi
 PROTOC_OS="$(uname -s)"
 PROTOC_ARCH="$(uname -m)"
 case "${PROTOC_OS}" in
@@ -27,6 +30,6 @@ if [[ "$(${PROTOC} --version 2>/dev/null)" != "libprotoc 3.${PROTOC_VERSION}" ]]
   rm -rf ./.tmp/protoc
   mkdir -p .tmp/protoc
   curl -L "https://github.com/google/protobuf/releases/download/v${PROTOC_VERSION}/protoc-${PROTOC_VERSION}-${PROTOC_OS}-${PROTOC_ARCH}.zip" > .tmp/protoc/protoc.zip
-  cd ./.tmp/protoc && unzip protoc.zip && cd ..
+  pushd ./.tmp/protoc && unzip protoc.zip && popd
 fi