diff --git a/scripts/tools/gpu-intel.func b/scripts/tools/gpu-intel.func
index 0b91a48..0730a1f 100644
--- a/scripts/tools/gpu-intel.func
+++ b/scripts/tools/gpu-intel.func
@@ -64,11 +64,16 @@ function install_intel_tools_in_ct() {
 
     if [[ "$install_nonfree" == "yes" ]]; then
         msg info "Enabling non-free sources in $ctid..."
-        pct exec "$ctid" -- bash -c "tee /etc/apt/sources.list.d/non-free.list >/dev/null" <<'EOF'
+
+        pct exec "$ctid" -- bash -c '
+      grep -q "non-free" /etc/apt/sources.list && exit 0
+
+      cat <<EOF > /etc/apt/sources.list.d/non-free.list
 deb http://deb.debian.org/debian bookworm main contrib non-free non-free-firmware
 deb http://deb.debian.org/debian-security bookworm-security main contrib non-free non-free-firmware
 deb http://deb.debian.org/debian bookworm-updates main contrib non-free non-free-firmware
 EOF
+    '
     fi
 
     msg info "Installing Intel tools in CT $ctid..."