diff --git a/common.nix b/common.nix
index c148422..35c5c48 100644
--- a/common.nix
+++ b/common.nix
@@ -1,4 +1,4 @@
-{ pkgs, ... }:
+{ pkgs, config, ... }:
 
 # Shared base for all hosts: user, SSH hardening, nix settings, packages.
 {
@@ -99,6 +99,8 @@
 
   # ---- Locale / firewall base ----
   time.timeZone = "Europe/Berlin";
+  # Flatpak needs /etc/timezone, falls back to UTC if not set.
+  environment.etc."timezone".text = config.time.timeZone;
   i18n.defaultLocale = "en_US.UTF-8";
   console.keyMap = "de";