diff --git a/.gitea/workflows/ci.yml b/.gitea/workflows/ci.yml
index c71e69d..e2f3fd7 100644
--- a/.gitea/workflows/ci.yml
+++ b/.gitea/workflows/ci.yml
@@ -419,10 +419,23 @@ jobs:
 
       - name: Validate backend (imports and app instantiation)
         run: |
-          # Install Python 3.12 (required for modern type hints like str | None)
-          apt-get update && apt-get install -y software-properties-common
-          add-apt-repository -y ppa:deadsnakes/ppa
-          apt-get update && apt-get install -y python3.12 python3.12-venv python3.12-dev
+          # Install Python 3.12 using pyenv (required for modern type hints like str | None)
+          # Debian Bullseye doesn't have Python 3.12 in default repos, so we use pyenv
+          apt-get update && apt-get install -y \
+            make build-essential libssl-dev zlib1g-dev \
+            libbz2-dev libreadline-dev libsqlite3-dev wget curl llvm \
+            libncursesw5-dev xz-utils tk-dev libxml2-dev libxmlsec1-dev \
+            libffi-dev liblzma-dev git
+          
+          # Install pyenv
+          export PYENV_ROOT="/opt/pyenv"
+          export PATH="$PYENV_ROOT/bin:$PATH"
+          curl https://pyenv.run | bash
+          
+          # Install Python 3.12 using pyenv
+          eval "$(pyenv init -)"
+          pyenv install -v 3.12.7
+          pyenv global 3.12.7
           
           # Create virtual environment with Python 3.12
           python3.12 -m venv /tmp/backend-venv