diff --git a/.gitea/workflows/docker-image.yml b/.gitea/workflows/docker-image.yml
index 035f0c0..a0cd50e 100644
--- a/.gitea/workflows/docker-image.yml
+++ b/.gitea/workflows/docker-image.yml
@@ -2,7 +2,7 @@ name: build-docker-image
 
 on:
   push:
-    branches: [ "main" ]
+    branches: [ "master" ]
   workflow_dispatch:
 
 env:
@@ -22,7 +22,9 @@ jobs:
         uses: actions/checkout@v4
 
       - name: Short SHA
-        run: echo "SHORT_SHA=${GITHUB_SHA::7}" >> $GITHUB_ENV
+        run: |
+          SHORT_SHA="$(printf '%.7s' "$GITHUB_SHA")"
+          echo "SHORT_SHA=$SHORT_SHA" >> "$GITHUB_ENV"
 
       - name: Set up Docker Buildx
         uses: docker/setup-buildx-action@v3