diff --git a/.drone.yml b/.drone.yml
index 8af4c79..991956d 100644
--- a/.drone.yml
+++ b/.drone.yml
@@ -4,7 +4,7 @@ name: build
 
 steps:
 - name: build-deb
-  image: ubuntu:22.04
+  image: cache.coadcorp.com/ubuntu:22.04
   environment:
     DEBIAN_FRONTEND: noninteractive
   commands:
@@ -14,7 +14,7 @@ steps:
   - ls -la dist
 
 - name: gitea-release
-  image: plugins/gitea-release
+  image: cache.coadcorp.com/plugins/gitea-release
   depends_on:
   - build-deb
   settings:
diff --git a/sbin/build_deb.sh b/sbin/build_deb.sh
index fd01cde..97022cd 100644
--- a/sbin/build_deb.sh
+++ b/sbin/build_deb.sh
@@ -5,6 +5,10 @@ set -euo pipefail
 ROOT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")/.." && pwd)"
 VERSION="${1:-${VERSION:-0.0.0}}"
 VERSION="${VERSION#v}"
+# Debian versions must start with a digit; fall back to 0.0.0+<sha/tag>.
+if [[ ! "$VERSION" =~ ^[0-9] ]]; then
+  VERSION="0.0.0+${VERSION}"
+fi
 ARCH="${ARCH:-$(dpkg --print-architecture)}"
 
 PACKAGE_NAME="slide"