diff --git a/app/components/__tests__/OrganizationSwitcher.spec.ts b/app/components/__tests__/OrganizationSwitcher.spec.ts
index 752ba5c..90ce996 100644
--- a/app/components/__tests__/OrganizationSwitcher.spec.ts
+++ b/app/components/__tests__/OrganizationSwitcher.spec.ts
@@ -14,20 +14,23 @@ const mockOrganizations = [
 // For now, the component is indirectly tested through useOrganizationSelector tests
 // and manual testing shows it works correctly
 
+// vi.mock is hoisted above the imports and the factory runs once, on the first
+// import of the mocked module -- it was never re-applied per test despite sitting
+// in beforeEach. vitest 5 rejects the nested call outright rather than silently
+// hoisting it, so declare it where it actually executes.
+vi.mock('~/composables/useOrganizationSelector', () => ({
+  useOrganizationSelector: () => ({
+    organizations: ref([mockOrganizations[0]]),
+    selectedOrganization: ref(mockOrganizations[0]),
+    selectedOrgId: ref('1'),
+    selectOrganization: mockSelectOrganization,
+  }),
+}))
+
 describe('OrganizationSwitcher - Single Organization', () => {
   beforeEach(() => {
     vi.resetModules()
     mockSelectOrganization.mockClear()
-
-    // Mock with single organization
-    vi.mock('~/composables/useOrganizationSelector', () => ({
-      useOrganizationSelector: () => ({
-        organizations: ref([mockOrganizations[0]]),
-        selectedOrganization: ref(mockOrganizations[0]),
-        selectedOrgId: ref('1'),
-        selectOrganization: mockSelectOrganization,
-      }),
-    }))
   })
 
   it('should show a chip for single organization', async () => {
diff --git a/test/setup.ts b/test/setup.ts
index 8da6362..85185ca 100644
--- a/test/setup.ts
+++ b/test/setup.ts
@@ -31,7 +31,15 @@ class LocalStorageMock {
   }
 }
 
-global.localStorage = new LocalStorageMock() as unknown as Storage
+// jsdom defines localStorage as a getter-only accessor on the window object, so a
+// plain assignment throws ("Cannot set property localStorage ... which has only a
+// getter") under vitest 5, which no longer shadows it with a writable global.
+// defineProperty replaces the accessor outright and works on both.
+Object.defineProperty(globalThis, 'localStorage', {
+  value: new LocalStorageMock() as unknown as Storage,
+  writable: true,
+  configurable: true,
+})
 
 // Make Vue composables globally available
 global.ref = Vue.ref