diff --git a/tests/e2e/cli-sync-option-routing.e2e.test.ts b/tests/e2e/cli-sync-option-routing.e2e.test.ts
index 2d6927d..6987759 100644
--- a/tests/e2e/cli-sync-option-routing.e2e.test.ts
+++ b/tests/e2e/cli-sync-option-routing.e2e.test.ts
@@ -78,6 +78,10 @@ describe('CLI sync option routing E2E', () => {
         DEEPL_API_KEY: 'mock-api-key-for-testing:fx',
         NO_COLOR: '1',
         CI: undefined,
+        // Ambient NODE_OPTIONS can make node print warnings to stderr, which
+        // the JSON-envelope assertions parse.
+        NODE_OPTIONS: undefined,
+        NODE_NO_WARNINGS: '1',
       },
       stdio: ['ignore', 'pipe', 'pipe'],
       timeout: 15000,