diff --git a/rebuild-image b/rebuild-image
new file mode 100755
index 000000000..1842e572f
--- /dev/null
+++ b/rebuild-image
@@ -0,0 +1,47 @@
+#!/bin/bash
+# Rebuild a cached docker image if the input files have changed.
+# Usage: ./rebuild-image <image name> <image dir> <image files...>
+
+set -eux
+
+IMAGENAME=$1 # no dashes in the name please!
+IMAGEDIR=$2
+shift 2
+
+INPUTFILES=$@
+CACHEDIR=$HOME/docker/
+
+# Rebuild the image
+rebuild() {
+    mkdir -p $CACHEDIR
+    rm $CACHEDIR/$IMAGENAME* || true
+    docker build -t $IMAGENAME $IMAGEDIR
+	docker save $IMAGENAME:latest > $CACHEDIR/image-$CIRCLE_SHA1
+}
+
+# Get the revision the cached image was build at
+cached_image_rev() {
+	find $CACHEDIR -name '$IMAGENAME-*' -type f | sed 's/[^\-]*\-//'
+}
+
+# Have there been any revision beween $1 and $2
+has_changes() {
+	local rev1=$1
+	local rev2=$2
+	local changes=$(git log --oneline $rev1..$rev2 -- $INPUTFILES | wc -l)
+	[ "$changes" -gt 0 ]
+}
+
+cached_revision=$(cached_image_rev)
+if [ -z "$cached_revision" ]; then
+	rebuild
+	exit 0
+fi
+
+if has_changes $cached_revision $CIRCLE_SHA1 ; then
+	rebuild
+	exit 0
+fi
+
+# we didn't rebuild; import cached version
+docker load -i $CACHEDIR/$IMAGENAME-*