diff --git a/README.md b/README.md
index db46f87..c27bfe3 100644
--- a/README.md
+++ b/README.md
@@ -80,6 +80,13 @@ The following environment variables are supported:
    will not be included in the image, making it safe to use an `apt-cacher` or
    similar package for development.
 
+ * `TEMP_REPO` (Default: unset)
+
+   An additional temporary apt repo to be used during the build process. This
+   could be useful if you require pre-release software to be included in the
+   image. The variable should contain sources in [one-line-style format](https://manpages.debian.org/stable/apt/sources.list.5.en.html#ONE-LINE-STYLE_FORMAT).
+   "RELEASE" will be replaced with the RELEASE variable.
+
  * `BASE_DIR`  (Default: location of `build.sh`)
 
    **CAUTION**: Currently, changing this value will probably break build.sh
diff --git a/build.sh b/build.sh
index f35da03..4d3902c 100755
--- a/build.sh
+++ b/build.sh
@@ -222,6 +222,7 @@ export PUBKEY_SSH_FIRST_USER
 
 export CLEAN
 export APT_PROXY
+export TEMP_REPO
 
 export STAGE
 export STAGE_DIR
diff --git a/export-image/02-set-sources/01-run.sh b/export-image/02-set-sources/01-run.sh
index 6d50496..d93efdf 100755
--- a/export-image/02-set-sources/01-run.sh
+++ b/export-image/02-set-sources/01-run.sh
@@ -1,6 +1,7 @@
 #!/bin/bash -e
 
 rm -f "${ROOTFS_DIR}/etc/apt/apt.conf.d/51cache"
+rm -f "${ROOTFS_DIR}/etc/apt/sources.list.d/00-temp.list"
 find "${ROOTFS_DIR}/var/lib/apt/lists/" -type f -delete
 on_chroot << EOF
 apt-get update
diff --git a/stage0/00-configure-apt/00-run.sh b/stage0/00-configure-apt/00-run.sh
index 926c4c6..1b7e03f 100755
--- a/stage0/00-configure-apt/00-run.sh
+++ b/stage0/00-configure-apt/00-run.sh
@@ -12,6 +12,13 @@ else
 	rm -f "${ROOTFS_DIR}/etc/apt/apt.conf.d/51cache"
 fi
 
+if [ -n "$TEMP_REPO" ]; then
+	install -m 644 /dev/null "${ROOTFS_DIR}/etc/apt/sources.list.d/00-temp.list"
+	echo "$TEMP_REPO" | sed "s/RELEASE/$RELEASE/g" > "${ROOTFS_DIR}/etc/apt/sources.list.d/00-temp.list"
+else
+	rm -f "${ROOTFS_DIR}/etc/apt/sources.list.d/00-temp.list"
+fi
+
 cat files/raspberrypi.gpg.key | gpg --dearmor > "${STAGE_WORK_DIR}/raspberrypi-archive-stable.gpg"
 install -m 644 "${STAGE_WORK_DIR}/raspberrypi-archive-stable.gpg" "${ROOTFS_DIR}/etc/apt/trusted.gpg.d/"
 on_chroot <<- \EOF