diff --git a/.gitea/workflows/backend-docker.yml b/.gitea/workflows/backend-docker.yml
index e8c5e18..9cb7751 100644
--- a/.gitea/workflows/backend-docker.yml
+++ b/.gitea/workflows/backend-docker.yml
@@ -116,6 +116,7 @@ jobs:
           REGISTRY_TOKEN: ${{ secrets.REGISTRY_TOKEN }}
           BUILTIN_GITEA_TOKEN: ${{ secrets.GITEA_TOKEN }}
           GITHUB_ACTOR_NAME: ${{ github.actor }}
+          GITHUB_REPOSITORY_OWNER_NAME: ${{ github.repository_owner }}
         run: |
           set -euo pipefail
 
@@ -123,21 +124,43 @@ jobs:
           CUSTOM_REGISTRY_TOKEN="${REGISTRY_TOKEN:-}"
           BUILTIN_REGISTRY_TOKEN="${BUILTIN_GITEA_TOKEN:-}"
           ACTOR_USER="${GITHUB_ACTOR_NAME:-}"
+          OWNER_USER="${GITHUB_REPOSITORY_OWNER_NAME:-}"
 
           if [ -n "${CUSTOM_REGISTRY_TOKEN}" ]; then
-            REGISTRY_USER="${CUSTOM_REGISTRY_USER:-${ACTOR_USER}}"
             REGISTRY_TOKEN="${CUSTOM_REGISTRY_TOKEN}"
           else
-            REGISTRY_USER="${ACTOR_USER:-${CUSTOM_REGISTRY_USER}}"
             REGISTRY_TOKEN="${BUILTIN_REGISTRY_TOKEN}"
           fi
 
-          if [ -z "${REGISTRY_USER}" ] || [ -z "${REGISTRY_TOKEN}" ]; then
+          if [ -z "${REGISTRY_TOKEN}" ]; then
             echo "Missing registry credentials: set REGISTRY_USERNAME/REGISTRY_TOKEN, or rely on the built-in GITEA_TOKEN with packages:write permission."
             exit 1
           fi
 
-          echo "${REGISTRY_TOKEN}" | docker login "${REGISTRY_HOST}" --username "${REGISTRY_USER}" --password-stdin
+          CANDIDATE_USERS=()
+          for candidate in "${CUSTOM_REGISTRY_USER}" "${ACTOR_USER}" "${OWNER_USER}"; do
+            if [ -n "${candidate}" ] && [[ ! " ${CANDIDATE_USERS[*]} " =~ [[:space:]]${candidate}[[:space:]] ]]; then
+              CANDIDATE_USERS+=("${candidate}")
+            fi
+          done
+
+          if [ ${#CANDIDATE_USERS[@]} -eq 0 ]; then
+            echo "Missing registry username: set REGISTRY_USERNAME or ensure github.actor/repository_owner are available."
+            exit 1
+          fi
+
+          LOGIN_OK=0
+          for candidate in "${CANDIDATE_USERS[@]}"; do
+            if echo "${REGISTRY_TOKEN}" | docker login "${REGISTRY_HOST}" --username "${candidate}" --password-stdin; then
+              LOGIN_OK=1
+              break
+            fi
+          done
+
+          if [ "${LOGIN_OK}" -ne 1 ]; then
+            echo "Registry login failed for all candidate usernames."
+            exit 1
+          fi
 
       - name: Build image
         shell: bash