diff --git a/app/assets/javascripts/discourse/app/helpers/theme-i18n.js b/app/assets/javascripts/discourse/app/helpers/theme-i18n.js
index 11fffb8522b..5756eca4a36 100644
--- a/app/assets/javascripts/discourse/app/helpers/theme-i18n.js
+++ b/app/assets/javascripts/discourse/app/helpers/theme-i18n.js
@@ -3,5 +3,12 @@ import I18n from "discourse-i18n";
 
 registerRawHelper("theme-i18n", themeI18n);
 export default function themeI18n(themeId, key, params) {
+  if (typeof themeId !== "number") {
+    throw new Error(
+      `The theme-i18n helper is not supported in this context.\n\n` +
+        `In a theme .gjs file, use '{{i18n (themePrefix "${themeId}")}}' instead.\n\n` +
+        `'themePrefix' is available automatically, and does not need to be imported.\n`
+    );
+  }
   return I18n.t(`theme_translations.${themeId}.${key}`, params);
 }
diff --git a/app/assets/javascripts/discourse/app/helpers/theme-setting.js b/app/assets/javascripts/discourse/app/helpers/theme-setting.js
index 8c3b08275e9..870ff0de51b 100644
--- a/app/assets/javascripts/discourse/app/helpers/theme-setting.js
+++ b/app/assets/javascripts/discourse/app/helpers/theme-setting.js
@@ -3,5 +3,12 @@ import { registerRawHelper } from "discourse-common/lib/helpers";
 
 registerRawHelper("theme-setting", themeSetting);
 export default function themeSetting(themeId, key) {
+  if (typeof themeId !== "number") {
+    throw new Error(
+      `The theme-setting helper is not supported in this context.\n\n` +
+        `In a theme .gjs file, use '{{settings.${themeId}}}' instead.\n\n` +
+        `'settings' is available automatically, and does not need to be imported.\n`
+    );
+  }
   return getThemeSetting(themeId, key);
 }