diff --git a/nixos/modules/config/i18n.nix b/nixos/modules/config/i18n.nix
index cc2ddda9d32f..feb76581a720 100644
--- a/nixos/modules/config/i18n.nix
+++ b/nixos/modules/config/i18n.nix
@@ -68,7 +68,8 @@ with lib;
   config = {
 
     environment.systemPackages =
-      optional (config.i18n.supportedLocales != []) config.i18n.glibcLocales;
+      # We increase the priority a little, so that plain glibc in systemPackages can't win.
+      optional (config.i18n.supportedLocales != []) (lib.setPrio (-1) config.i18n.glibcLocales);
 
     environment.sessionVariables =
       { LANG = config.i18n.defaultLocale;