diff --git a/scripts/fdroid-publish.sh b/scripts/fdroid-publish.sh
index 8fcc0a6..f053c0f 100755
--- a/scripts/fdroid-publish.sh
+++ b/scripts/fdroid-publish.sh
@@ -15,7 +15,8 @@
 #
 # Environment:
 #   MTGC_FDROID_DIR   repo directory, if not given as an argument
-#   FDROID_REPO_URL   public address of <dir>/repo; only needed the first time, to create the repo
+#   FDROID_REPO_URL   public address of <dir>/repo, ending in /repo; needed the first time,
+#                     and changes the repo's address if set later
 #   MTGC_ANDROID_KEYSTORE  where --init-keystore puts the key (default ~/.local/share/mtgc/android-release.jks)
 #
 # Serve <dir>/repo (and <dir>/archive if you like), never <dir> itself: it holds
@@ -25,7 +26,7 @@
 set -euo pipefail
 
 usage() {
-    sed -n '3,23p' "$0" | sed 's/^# \{0,1\}//'
+    sed -n '3,24p' "$0" | sed 's/^# \{0,1\}//'
     exit "${1:-0}"
 }
 
@@ -120,8 +121,14 @@ fi
 
 # --- 4. The repo, the first time --------------------------------------------
 
+repo_url="${FDROID_REPO_URL%/}"
+case "$repo_url" in
+    "" | */repo) ;;
+    *) err "FDROID_REPO_URL must end in /repo (fdroidserver requires it), e.g. $repo_url/repo"; exit 1 ;;
+esac
+
 if [ ! -f "$dir/config.yml" ]; then
-    if [ -z "${FDROID_REPO_URL:-}" ]; then
+    if [ -z "$repo_url" ]; then
         err "no F-Droid repo in $dir yet; set FDROID_REPO_URL to the address $dir/repo will be served at"
         exit 1
     fi
@@ -129,7 +136,7 @@ if [ ! -f "$dir/config.yml" ]; then
     (cd "$dir" && fdroid init --android-home "$ANDROID_HOME" --no-prompt -q)
     cat >>"$dir/config.yml" <<EOF
 
-repo_url: ${FDROID_REPO_URL%/}
+repo_url: $repo_url
 repo_name: mtgc
 repo_description: >-
   Releases of mtgc, a personal Magic: The Gathering library catalog.
@@ -138,6 +145,11 @@ EOF
     # `fdroid update` copies this into repo/icons/ itself.
     cp src-tauri/icons/icon.png "$dir/icon.png"
 fi
+# A later FDROID_REPO_URL moves the repo to a new address.
+if [ -n "$repo_url" ] && ! grep -qxF "repo_url: $repo_url" "$dir/config.yml"; then
+    info "setting repo_url to $repo_url"
+    sed -i "s|^repo_url:.*|repo_url: $repo_url|" "$dir/config.yml"
+fi
 
 if [ ! -f "$dir/metadata/$APP_ID.yml" ]; then
     mkdir -p "$dir/metadata"
@@ -198,9 +210,15 @@ esac
 
 # --- 7. Publish -------------------------------------------------------------
 
-cp "$apk" "$dir/repo/${APP_ID}_${version_code}.apk"
+published="$dir/repo/${APP_ID}_${version_code}.apk"
+cp "$apk" "$published"
 info "updating the repo index"
-(cd "$dir" && fdroid update -q)
+if ! (cd "$dir" && fdroid update -q); then
+    # Take the APK back out, or the next run would think it's already published.
+    rm -f "$published"
+    err "fdroid update failed; nothing was published"
+    exit 1
+fi
 
 # --- 8. Where to point F-Droid ----------------------------------------------