diff --git a/ts/core/MathDocument.ts b/ts/core/MathDocument.ts
index aa250aed7..60d722759 100644
--- a/ts/core/MathDocument.ts
+++ b/ts/core/MathDocument.ts
@@ -37,6 +37,7 @@ import { DOMAdaptor } from '../core/DOMAdaptor.js';
 import { BitField, BitFieldClass } from '../util/BitField.js';
 import { PrioritizedList } from '../util/PrioritizedList.js';
 import { handleRetriesFor } from '../util/Retries.js';
+import { Locale } from '../util/Locale.js';
 
 /*****************************************************************/
 
@@ -771,6 +772,12 @@ export abstract class AbstractMathDocument<N, T, D> implements MathDocument<
    * @class
    */
   constructor(document: D, adaptor: DOMAdaptor<N, T, D>, options: OptionList) {
+    if (!Locale.initialized) {
+      // FIXME: add URL when we have one.
+      console.error(
+        'MathJax locales not loaded.  You may receive cryptic error messages.'
+      );
+    }
     const CLASS = this.constructor as typeof AbstractMathDocument;
     this.document = document;
     this.options = userOptions(defaultOptions({}, CLASS.OPTIONS), options);
diff --git a/ts/util/Locale.ts b/ts/util/Locale.ts
index e7b5ade36..ae1628717 100644
--- a/ts/util/Locale.ts
+++ b/ts/util/Locale.ts
@@ -35,6 +35,10 @@ export type namedData = { [name: string | number]: string };
  * The Locale class for handling localized messages
  */
 export class Locale {
+  /**
+   * Whether setLocale() has been called or not.
+   */
+  public static initialized = false;
   /**
    * The current locale
    */
@@ -251,6 +255,7 @@ export class Locale {
   public static async setLocale(
     locale: string = this.current
   ): Promise<void[]> {
+    this.initialized = true;
     this.current = locale;
     const promises = [];
     for (const [component, [directory, loaded]] of Object.entries(