diff --git a/Makefile b/Makefile
index aecf598..1cdc172 100644
--- a/Makefile
+++ b/Makefile
@@ -33,6 +33,7 @@ IMAGE_NAME        := maas-rack-controller maas-region-controller sstream-cache
 BUILD_DIR         := $(shell mktemp -d)
 HELM              := $(BUILD_DIR)/helm
 SSTREAM_IMAGE     := "https://images.maas.io/ephemeral-v3/daily/"
+SSTREAM_RELEASE   := "xenial"
 UBUNTU_BASE_IMAGE ?= ubuntu:16.04
 
 .PHONY: images
@@ -82,6 +83,7 @@ ifeq ($(USE_PROXY), true)
 		--build-arg no_proxy=$(NO_PROXY) \
 		--build-arg NO_PROXY=$(NO_PROXY) \
 		--build-arg SSTREAM_IMAGE=$(SSTREAM_IMAGE) \
+		--build-arg SSTREAM_RELEASE=$(SSTREAM_RELEASE) \
 		$(IMAGE_DIR)
 else
 	docker build -t $(IMAGE) --label $(LABEL) --network=host \
@@ -91,6 +93,7 @@ else
 		-f $(IMAGE_DIR)/Dockerfile \
 		--build-arg FROM=$(UBUNTU_BASE_IMAGE) \
 		--build-arg SSTREAM_IMAGE=$(SSTREAM_IMAGE) \
+		--build-arg SSTREAM_RELEASE=$(SSTREAM_RELEASE) \
 		$(IMAGE_DIR)
 endif
 ifeq ($(PUSH_IMAGE), true)
diff --git a/images/sstream-cache/Dockerfile b/images/sstream-cache/Dockerfile
index 18d249d..d840a33 100644
--- a/images/sstream-cache/Dockerfile
+++ b/images/sstream-cache/Dockerfile
@@ -9,7 +9,7 @@ LABEL org.opencontainers.image.vendor='The Airship Authors'
 LABEL org.opencontainers.image.licenses='Apache-2.0'
 
 ARG SSTREAM_IMAGE=https://images.maas.io/ephemeral-v3/daily/
-ENV IMAGE_SRC ${SSTREAM_IMAGE}
+ARG SSTREAM_RELEASE=xenial
 
 RUN apt-get -qq update && \
     apt install -y simplestreams \
@@ -19,10 +19,10 @@ RUN apt-get -qq update && \
                    python-certifi --no-install-recommends \
                    file
 
-RUN sstream-mirror --keyring=/usr/share/keyrings/ubuntu-cloudimage-keyring.gpg $IMAGE_SRC \
-    /var/www/html/maas/images/ephemeral-v3/daily 'arch=amd64' 'release~xenial' --max=1 --progress
+RUN sstream-mirror --keyring=/usr/share/keyrings/ubuntu-cloudimage-keyring.gpg ${SSTREAM_IMAGE} \
+    /var/www/html/maas/images/ephemeral-v3/daily 'arch=amd64' "release~${SSTREAM_RELEASE}" --max=1 --progress
 
-RUN sstream-mirror --keyring=/usr/share/keyrings/ubuntu-cloudimage-keyring.gpg $IMAGE_SRC \
+RUN sstream-mirror --keyring=/usr/share/keyrings/ubuntu-cloudimage-keyring.gpg ${SSTREAM_IMAGE} \
    /var/www/html/maas/images/ephemeral-v3/daily 'os~(grub*|pxelinux)' --max=1 --progress
 
 RUN sh -c 'echo "" > /etc/apache2/ports.conf'