diff --git a/test/utils/test-setup.ts b/test/utils/test-setup.ts
index c03a696d6..95ae4b8df 100644
--- a/test/utils/test-setup.ts
+++ b/test/utils/test-setup.ts
@@ -2,6 +2,9 @@ import "source-map-support/register"
 import "reflect-metadata"
 import * as chai from "chai"
 
+// Tests assume UTC time zone when formatting/parsing dates.
+process.env.TZ = "UTC"
+
 chai.should()
 chai.use(require("sinon-chai"))
 chai.use(require("chai-as-promised"))