diff --git a/build.sh b/build.sh
index 0535161..88c3172 100755
--- a/build.sh
+++ b/build.sh
@@ -6,8 +6,17 @@ docker build -t ungleich-hardware .
 
 while [ $# -ge 1 ]; do
     tag=$1; shift
-    git tag -a -m "Version $tag" $tag
-    git push --tags
+    # Does the tag exist?
+    if git rev-list "$tag" 2>/dev/null; then
+        cur=$(git describe)
+        if [ $cur != $tag ]; then
+            echo "Requested build for $tag, but we are on $cur, aborting"
+            exit 1
+        fi
+    else
+        git tag -a -m "Version $tag" $tag
+        git push --tags
+    fi
     docker tag ungleich-hardware:latest ungleich/ungleich-hardware:${tag}
     docker tag ungleich-hardware:latest harbor.ungleich.svc.p10.k8s.ooo/ungleich-public/ungleich-hardware:${tag}
     docker push ungleich/ungleich-hardware:${tag}