diff --git a/.gitea/workflows/build.yml b/.gitea/workflows/build.yml
index bd0bc66e..4b2850d1 100644
--- a/.gitea/workflows/build.yml
+++ b/.gitea/workflows/build.yml
@@ -25,33 +25,28 @@ jobs:
       - name: Checkout código
         uses: actions/checkout@v4
 
-      - name: Configurar Python
-        uses: actions/setup-python@v5
-        with:
-          python-version: "3.11"
-          cache: "pip"
-          cache-dependency-path: backend/requirements.txt
-
-      - name: Instalar dependencias del backend
-        run: |
-          python -m pip install --upgrade pip
-          pip install -r backend/requirements.txt
-
-      - name: Comprobar TEST_DATABASE_URL
+      # No usamos actions/setup-python: en runners self-hosted (Debian) suele fallar
+      # al descargar versiones desde el manifest. Se usa python3 del sistema + venv.
+      - name: Instalar dependencias y ejecutar tests del backend
         env:
           TEST_DATABASE_URL: ${{ secrets.TEST_DATABASE_URL }}
         run: |
+          set -e
           if [ -z "$TEST_DATABASE_URL" ]; then
             echo "::error::Define el secret TEST_DATABASE_URL en el repo (Gitea → Ajustes → Secretos)."
             echo "Ejemplo: postgresql://usuario:clave@host:5432/nombre_bd"
             exit 1
           fi
-
-      - name: Ejecutar tests del backend
-        env:
-          TEST_DATABASE_URL: ${{ secrets.TEST_DATABASE_URL }}
-        working-directory: backend
-        run: pytest -q tests
+          python3 --version
+          if ! python3 -m venv "$GITHUB_WORKSPACE/.pytest-venv" 2>/dev/null; then
+            echo "python3 -m venv falló. En Debian/Ubuntu instala: sudo apt-get install -y python3-venv"
+            exit 1
+          fi
+          . "$GITHUB_WORKSPACE/.pytest-venv/bin/activate"
+          python -m pip install --upgrade pip
+          pip install -r "$GITHUB_WORKSPACE/backend/requirements.txt"
+          cd "$GITHUB_WORKSPACE/backend"
+          pytest -q tests
 
   build:
     runs-on: self-hosted