diff --git a/Dockerfile b/Dockerfile
index 578a3d5..dbadb55 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -16,6 +16,10 @@ RUN apt-get update && \
                        syslinux tree python3-pip bc python3-yaml \
                        lsb-release python3-setuptools ssh-client \
                        vim less mercurial && \
+    echo 'deb http://deb.debian.org/debian stretch main' >> /etc/apt/sources.list.d/backports.list && \
+    apt-get update && \
+    apt-get install -y -f --no-install-recommends --target-release stretch \
+            xz-utils && \
     apt-get clean && \
     rm -rf /var/lib/apt/lists/* /tmp/* /var/tmp/*
 
diff --git a/Dockerfile.isar b/Dockerfile.isar
index 8a77087..f46c890 100644
--- a/Dockerfile.isar
+++ b/Dockerfile.isar
@@ -2,11 +2,9 @@ FROM kasproject/kas:latest
 
 ENV DEBIAN_FRONTEND noninteractive
 
-RUN echo 'deb http://deb.debian.org/debian jessie-backports main' >> /etc/apt/sources.list.d/backports.list && \
-    echo 'deb http://deb.debian.org/debian stretch main' >> /etc/apt/sources.list.d/backports.list
-
 ENV LC_ALL=en_US.UTF-8
-RUN apt-get update && \
+RUN echo 'deb http://deb.debian.org/debian jessie-backports main' >> /etc/apt/sources.list.d/backports.list && \
+    apt-get update && \
     apt-get install -y -f --no-install-recommends --target-release jessie \
             autoconf automake gdisk libtool bash-completion \
             sudo grub2 grub-efi-amd64-bin grub-efi-ia32-bin qemu-user-static \