diff --git a/contrib/update-images.sh b/contrib/update-images.sh
index 5fb870478a087f07001f7e0a646d6162ab9f2d5e..318da84b5aedadf1941f08a4dc364a482a85000f 100755
--- a/contrib/update-images.sh
+++ b/contrib/update-images.sh
@@ -2,11 +2,12 @@
 
 set -e
 
-BASE_URL="https://firmware.darmstadt.freifunk.net/images/"
+BASE_URL=${BASE_URL:-"https://firmware.darmstadt.freifunk.net/images/"}
+BRANCHES=${BRANCHES:-"stable beta testing"}
 
-for BRANCH in "stable" "beta" "testing";
+for BRANCH in $BRANCHES;
 do
-	echo "updating ${BRANCH}"
+	echo "updating ${BRANCH} from ${BASE_URL}"
 
 	mkdir -p images/${BRANCH}