diff --git a/modules/i18n/input-method/fcitx5.nix b/modules/i18n/input-method/fcitx5.nix
index 99014a23c..b2f53c52c 100644
--- a/modules/i18n/input-method/fcitx5.nix
+++ b/modules/i18n/input-method/fcitx5.nix
@@ -215,6 +215,14 @@ in
       sessionSearchVariables.QT_PLUGIN_PATH = [ "${fcitx5Package}/${pkgs.qt6.qtbase.qtPluginPrefix}" ];
     };
 
+    # Make sure X11 GTK apps still use IM module.
+    # https://wiki.archlinux.org/title/Fcitx5#IM_modules
+    gtk = lib.optionalAttrs cfg.waylandFrontend {
+      gtk2.extraConfig = ''gtk-im-module="fcitx"'';
+      gtk3.extraConfig.gtk-im-module = "fcitx";
+      gtk4.extraConfig.gtk-im-module = "fcitx";
+    };
+
     xdg = {
       configFile.fcitx5 =
         let