diff --git a/src/common/models/locale/locale.mocha.ts b/src/common/models/locale/locale.mocha.ts
index 4916693ad..2ce93c481 100644
--- a/src/common/models/locale/locale.mocha.ts
+++ b/src/common/models/locale/locale.mocha.ts
@@ -33,6 +33,12 @@ describe("locale", () => {
       expect(locale).to.deep.equal(en_us);
     });
 
+    it("should return default locale if passed unrecognized base identifier", () => {
+      const locale = fromConfig({ base: "foobar" } as any);
+
+      expect(locale).to.deep.equal(en_us);
+    });
+
     it("should use base locale and override desired fields", () => {
       const locale = fromConfig({ base: "en-US", overrides: { weekStart: 42 } });
 
diff --git a/src/common/models/locale/locale.ts b/src/common/models/locale/locale.ts
index 278c1fdf2..0ffe34b56 100644
--- a/src/common/models/locale/locale.ts
+++ b/src/common/models/locale/locale.ts
@@ -14,7 +14,8 @@
  * limitations under the License.
  */
 
-import { isObject } from "../../utils/general/general";
+import { LOGGER } from "../../logger/logger";
+import { isObject, isTruthy } from "../../utils/general/general";
 
 const enUS: Locale = {
   shortDays: ["S", "M", "T", "W", "T", "F", "S"],
@@ -48,6 +49,10 @@ export interface Locale {
 export function fromConfig(locale?: LocaleJS): Locale {
   if (!isObject(locale)) return DEFAULT_LOCALE;
   const { base, overrides } = locale;
+  if (!isTruthy(LOCALES[base])) {
+    LOGGER.warn(`Unsupported locale identifier: ${base}. Fallback to en-US.`);
+    return DEFAULT_LOCALE;
+  }
   return {
     ...LOCALES[base],
     ...overrides