diff --git a/Dockerfile b/Dockerfile
index 25b4470..fba739f 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -4,8 +4,8 @@ FROM ${BASE_IMAGE}:${ALPINE_VERSION}
 MAINTAINER "f <f@sutty.nl>"
 
 ENV PLATFORM=x86_64-linux-musl
-ENV GEM=none
-ENV VERSION=0
+ENV GEM_NAME=none
+ENV GEM_VERSION=0
 ENV SUTTY=sutty.nl
 ENV HTTP_BASIC_USER=sutty
 ENV HTTP_BASIC_PASSWORD=gibberish
diff --git a/bootstrap.sh b/bootstrap.sh
index 30e8434..126c5be 100755
--- a/bootstrap.sh
+++ b/bootstrap.sh
@@ -2,5 +2,6 @@
 set -e
 
 test -n "${EXTRA_PKGS}" && apk add --no-cache ${EXTRA_PKGS}
+test -n "${EXTRA_GEMS}" && gem install --no-user-install --no-document ${EXTRA_GEMS}
 
 su-exec builder /usr/local/bin/gem-compiler
diff --git a/bulk-compiler.sh b/bulk-compiler.sh
index 667256d..037d436 100755
--- a/bulk-compiler.sh
+++ b/bulk-compiler.sh
@@ -6,6 +6,8 @@ test -n "${HTTP_BASIC_PASSWORD}"
 test -n "${SUTTY}"
 test -n "${PLATFORM}"
 
+install -dm 755 -o builder -g builder cache gems
+
 find build/ -type f |
   sed -re "s|^build/([^/]+)/(.*)|&\tbuilt/${ALPINE_VERSION}/\1/\2\t\1\t\2|" |
   while read BUILD BUILT GEM_NAME GEM_VERSION; do
@@ -20,6 +22,7 @@ find build/ -type f |
     GEM_NAME="${GEM_NAME}" \
     GEM_VERSION="${GEM_VERSION}" \
     EXTRA_PKGS="${EXTRA_PKGS}" \
+    EXTRA_GEMS="${EXTRA_GEMS}" \
     /usr/local/bin/bootstrap
 
     dirname "${BUILT}" | xargs mkdir -p
diff --git a/gem-compiler.sh b/gem-compiler.sh
index de98aee..11fbc7e 100755
--- a/gem-compiler.sh
+++ b/gem-compiler.sh
@@ -8,7 +8,10 @@ test -n "${HTTP_BASIC_PASSWORD}"
 test -n "${SUTTY}"
 test -n "${PLATFORM}"
 
+cd cache/
 # TODO: Support multiple Alpine/Ruby versions
-gem fetch --source=https://gems.${SUTTY} --platform=ruby --version ${VERSION} ${GEM}
-gem compile -V --prune --strip "strip --strip-unneeded" "${GEM}-${VERSION}.gem"
-gem inabox -o "${GEM}-${VERSION}-${PLATFORM}.gem" --host https://${HTTP_BASIC_USER}:${HTTP_BASIC_PASSWORD}@gems.${SUTTY}
+gem fetch --source=https://gems.${SUTTY} --platform=ruby --version ${GEM_VERSION} ${GEM_NAME}
+
+cd ../gems/
+gem compile -V --prune --strip "strip --strip-unneeded" "../cache/${GEM_NAME}-${GEM_VERSION}.gem"
+gem inabox -o "${GEM_NAME}-${GEM_VERSION}-${PLATFORM}.gem" --host https://${HTTP_BASIC_USER}:${HTTP_BASIC_PASSWORD}@gems.${SUTTY}