diff --git a/vitest.config.ts b/vitest.config.ts
index d5a060c..a6d590e 100644
--- a/vitest.config.ts
+++ b/vitest.config.ts
@@ -4,7 +4,14 @@ import path from "node:path";
 // React only exposes `act` in its development build, so a shell with
 // NODE_ENV=production would break every component test. Vitest only sets
 // NODE_ENV when it is unset, so force it.
-process.env.NODE_ENV = "test";
+//
+// Next's `next/types/global` declares NODE_ENV on ProcessEnv as `readonly`,
+// so a plain `process.env.NODE_ENV = "test"` fails the type check that
+// `next build` runs over this file (tsconfig includes **/*.ts) and takes
+// the whole deployment down. Object.assign has no source-to-target
+// assignability constraint, so it compiles while still writing the value
+// through process.env's setter at runtime.
+Object.assign(process.env, { NODE_ENV: "test" });
 
 export default defineConfig({
   resolve: {