diff --git a/packages/@sanity/cli/test/setup.ts b/packages/@sanity/cli/test/setup.ts
index d29aa8d48..056f143e9 100644
--- a/packages/@sanity/cli/test/setup.ts
+++ b/packages/@sanity/cli/test/setup.ts
@@ -5,3 +5,18 @@ import {vi} from 'vitest'
  */
 // Mock open, to prevent it from opening a browser
 vi.mock('open')
+
+// `@oclif/core/lib/screen.js` reads `process.stdout.getWindowSize()` at module
+// init when `process.stdout.isTTY` is truthy. Vitest's stdout proxy doesn't
+// implement `getWindowSize`, so any test that flips `isTTY = true` before oclif
+// is loaded (e.g. `checkForUpdates.test.ts`) crashes the whole worker.
+// Provide a no-op shim once per worker so the eventual load is safe.
+for (const stream of [process.stdout, process.stderr] as const) {
+  if (typeof stream.getWindowSize !== 'function') {
+    Object.defineProperty(stream, 'getWindowSize', {
+      configurable: true,
+      value: () => [80, 24],
+      writable: true,
+    })
+  }
+}