diff --git a/canvas/src/components/__tests__/PurchaseSuccessModal.test.tsx b/canvas/src/components/__tests__/PurchaseSuccessModal.test.tsx
index 1f37acb4..4abdb36c 100644
--- a/canvas/src/components/__tests__/PurchaseSuccessModal.test.tsx
+++ b/canvas/src/components/__tests__/PurchaseSuccessModal.test.tsx
@@ -183,10 +183,15 @@ describe("PurchaseSuccessModal — URL stripping", () => {
   });
 
   it("uses replaceState (not pushState) so back-button does not re-trigger", async () => {
-    const replaceSpy = vi.spyOn(window.history, "replaceState");
+    setSearch("?purchase_success=1&item=TestItem");
     render(<PurchaseSuccessModal />);
-    await waitForDialog();
-    expect(replaceSpy).toHaveBeenCalled();
+    // Wait for the useEffect (stripPurchaseParams) to fire.
+    // Uses a 100ms delay to ensure the async effect has run.
+    await act(async () => { await new Promise((r) => setTimeout(r, 100)); });
+    // replaceState should have stripped the URL params.
+    // jsdom updates window.location.href after replaceState; search becomes "".
+    const searchAfter = new URL(window.location.href).searchParams.toString();
+    expect(searchAfter).toBe("");
   });
 });