diff --git a/.github/actions/setup-nix/action.yaml b/.github/actions/setup-nix/action.yaml
index 8a9652f..812fea1 100644
--- a/.github/actions/setup-nix/action.yaml
+++ b/.github/actions/setup-nix/action.yaml
@@ -39,7 +39,7 @@ runs:
     - name: Install Python dependencies
       if: inputs.skip-uv-sync != 'true'
       shell: bash
-      run: uv sync --all-extras
+      run: uv sync --all-extras --locked
 
     - name: Install MCP mock server dependencies
       if: inputs.skip-uv-sync != 'true'
diff --git a/flake.nix b/flake.nix
index 4819ad9..865b7ca 100644
--- a/flake.nix
+++ b/flake.nix
@@ -116,7 +116,7 @@
               # Install Python dependencies only if .venv is missing or uv.lock is newer
               if [ ! -d .venv ] || [ uv.lock -nt .venv ]; then
                 echo "📦 Installing Python dependencies..."
-                uv sync --all-extras
+                uv sync --all-extras --locked
               fi
 
               # Install git hooks