diff --git a/README.md b/README.md
index c59b61b..dcb7603 100644
--- a/README.md
+++ b/README.md
@@ -18,13 +18,11 @@ buckets. It gives you a way of deploying pre-built code to
 You probably want to use an [IAM key](http://aws.amazon.com/iam/) with limited
 access. This code only requires `s3:GetObject` access to files.
 
-If you don't want to check your IAM keys into revision control, you can use
-the [Heroku Labs user-env-compile feature](https://devcenter.heroku.com/articles/labs-user-env-compile)
-to store the keys in Heroku's config system. Note that this is a beta feature
-and Heroku may remove it at any time:
+If you don't want to check your IAM keys into revision control, you can store
+them in Heroku's config system. Keys specified in the .buildpack-s3-tarballs
+file have precedence over keys in the config system.
 
     $ heroku config:add BUILDPACK_URL=https://github.com/paulhammond/s3-tarball-buildpack.git
-    $ heroku labs:enable user-env-compile
     $ heroku config:add AWS_ACCESS_KEY_ID=AKIA0000000000000000
     $ heroku config:add AWS_SECRET_ACCESS_KEY=xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
 
diff --git a/bin/compile b/bin/compile
index ede320d..6856d37 100755
--- a/bin/compile
+++ b/bin/compile
@@ -1,11 +1,12 @@
 #!/bin/bash
-# bin/compile <build-dir> <cache-dir>
+# bin/compile <build-dir> <cache-dir> <env-dir>
 # See https://github.com/paulhammond/s3-tarball-buildpack for license and docs
 
 working=$(pwd)
 mkdir -p "$2"
 build=$(cd "$1/" && pwd)
 cache=$(cd "$2/" && pwd)
+env=$(cd "$3/" && pwd)
 
 # s3simple is a small, simple bash s3 client with minimal dependencies.
 # See http://github.com/paulhammond/s3simple for documentation and licence.
@@ -62,6 +63,12 @@ s3simple() {
 
 cd $build
 
+for e in AWS_ACCESS_KEY_ID AWS_SECRET_ACCESS_KEY; do
+  if [ -f $env/$e ]; then
+    export "$e=$(cat $env/$e)"
+  fi
+done
+
 while read line; do
 	case "$line" in
 		AWS_*=*)