diff --git a/js/package.json b/js/package.json
index 881d11db0..011a25477 100644
--- a/js/package.json
+++ b/js/package.json
@@ -5,7 +5,7 @@
   "scripts": {
     "serve": "vue-cli-service serve",
     "build": "yarn run build:assets && yarn run build:pictures",
-    "test:unit": "LANG=en_US.UTF-8 LANGUAGE=en_US:en LC_ALL=en_US.UTF-8 vue-cli-service test:unit",
+    "test:unit": "LANG=en_US.UTF-8 LANGUAGE=en_US:en LC_ALL=en_US.UTF-8 TZ=UTC vue-cli-service test:unit",
     "test:e2e": "vue-cli-service test:e2e",
     "lint": "vue-cli-service lint",
     "build:assets": "vue-cli-service build",
diff --git a/js/tests/unit/specs/mocks/event.ts b/js/tests/unit/specs/mocks/event.ts
index e1bcd0be9..b0b3f0d46 100644
--- a/js/tests/unit/specs/mocks/event.ts
+++ b/js/tests/unit/specs/mocks/event.ts
@@ -61,6 +61,7 @@ export const joinEventMock = {
   email: "some@email.tld",
   message: "a message long enough",
   locale: "en_US",
+  timezone: "UTC",
 };
 
 export const eventNoCommentThreadsMock = {