diff --git a/.gitea/workflows/docker.yml b/.gitea/workflows/docker.yml
index 8cd17de..70d33fa 100644
--- a/.gitea/workflows/docker.yml
+++ b/.gitea/workflows/docker.yml
@@ -29,10 +29,10 @@ jobs:
           platforms: linux/amd64,linux/arm64
 
           build-args: |
-            BUILD_IDENTIFIER=${{ github.sha[0:5] }}
+            BUILD_IDENTIFIER=${{ github.sha.substring(0, 5) }}
 
           tags: |
-            gitea.spilum.net/spilum.net/mtf-nlp:${{ github.ref_name }}-${{ github.sha[0:5] }}
+            gitea.spilum.net/spilum.net/mtf-nlp:${{ github.ref_name }}-${{ github.sha.substring(0, 5) }}
             gitea.spilum.net/spilum.net/mtf-nlp:${{ github.ref_name }}-latest
 
       - name: Log out from registry