diff --git a/test/components/structures/MatrixChat-test.tsx b/test/components/structures/MatrixChat-test.tsx
index e786370b7c..dd4ae5de64 100644
--- a/test/components/structures/MatrixChat-test.tsx
+++ b/test/components/structures/MatrixChat-test.tsx
@@ -61,6 +61,10 @@ jest.mock("matrix-js-sdk/src/oidc/authorize", () => ({
     completeAuthorizationCodeGrant: jest.fn(),
 }));
 
+// Stub out ThemeWatcher as the necessary bits for themes are done in element-web's index.html and thus are lacking here,
+// plus JSDOM's implementation of CSSStyleDeclaration has a bunch of differences to real browsers which cause issues.
+jest.mock("../../../src/settings/watchers/ThemeWatcher");
+
 /** The matrix versions our mock server claims to support */
 const SERVER_SUPPORTED_MATRIX_VERSIONS = ["v1.1", "v1.5", "v1.6", "v1.8", "v1.9"];