diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 6a142b7..1a29f67 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -31,6 +31,9 @@ jobs:
 
       - run: pnpm build
 
+      - name: Smoke-test built entrypoints load in raw Node
+        run: pnpm smoke
+
       - name: Check type exports (attw)
         run: pnpm check-exports
 
diff --git a/package.json b/package.json
index 7e179a7..aef7382 100644
--- a/package.json
+++ b/package.json
@@ -113,6 +113,7 @@
     "lint": "eslint src",
     "lint:fix": "eslint src --fix",
     "prepare": "simple-git-hooks",
+    "smoke": "node scripts/smoke-load.mjs",
     "test": "vitest run --project unit --project nestjs",
     "test:e2e": "vitest run --project e2e",
     "test:watch": "vitest --project unit --project nestjs",
diff --git a/scripts/smoke-load.mjs b/scripts/smoke-load.mjs
new file mode 100644
index 0000000..a48ff5b
--- /dev/null
+++ b/scripts/smoke-load.mjs
@@ -0,0 +1,59 @@
+// Loads every built entrypoint in a plain Node process — no transpiler in the
+// chain — to catch output that fails to parse/load as a real consumer would
+// (e.g. untranspiled decorator syntax; see issue #87). vitest can't catch this
+// because it re-transpiles imported modules through swc/esbuild.
+//
+// Entrypoints are derived from package.json `exports` so this stays in sync as
+// adapters are added. Run after `pnpm build`: `pnpm smoke`.
+
+import { createRequire } from 'node:module'
+import { dirname, resolve } from 'node:path'
+import { fileURLToPath, pathToFileURL } from 'node:url'
+import { readFileSync } from 'node:fs'
+
+const require = createRequire(import.meta.url)
+const root = resolve(dirname(fileURLToPath(import.meta.url)), '..')
+
+const pkg = JSON.parse(readFileSync(resolve(root, 'package.json'), 'utf8'))
+
+// Collect (subpath, format, absolute file) triples from every export condition
+// that points at a built .mjs/.cjs file.
+const targets = []
+for (const [subpath, entry] of Object.entries(pkg.exports ?? {})) {
+  if (typeof entry !== 'object') continue
+  const mjs = entry.import?.default
+  const cjs = entry.require?.default
+  if (mjs) targets.push({ subpath, format: 'esm', file: resolve(root, mjs) })
+  if (cjs) targets.push({ subpath, format: 'cjs', file: resolve(root, cjs) })
+}
+
+if (targets.length === 0) {
+  console.error(
+    'No entrypoints found in package.json exports — smoke test is testing nothing.',
+  )
+  process.exit(1)
+}
+
+const failures = []
+for (const { subpath, format, file } of targets) {
+  try {
+    if (format === 'esm') await import(pathToFileURL(file).href)
+    else require(file)
+    console.log(`ok   ${format.padEnd(3)} ${subpath}`)
+  } catch (err) {
+    console.error(`FAIL ${format.padEnd(3)} ${subpath}`)
+    console.error(`     ${err?.stack ?? err}`)
+    failures.push({ subpath, format, file })
+  }
+}
+
+if (failures.length > 0) {
+  console.error(
+    `\n${failures.length} built entrypoint(s) failed to load in raw Node.`,
+  )
+  process.exit(1)
+}
+
+console.log(
+  `\nAll ${targets.length} built entrypoints load cleanly in raw Node.`,
+)
diff --git a/src/adapters/nestjs/middleware.ts b/src/adapters/nestjs/middleware.ts
index c9447d8..929a07e 100644
--- a/src/adapters/nestjs/middleware.ts
+++ b/src/adapters/nestjs/middleware.ts
@@ -87,7 +87,11 @@ function toWebRequest(req: NestRequestLike): Request {
 export function withSupabase(
   config?: Omit<WithSupabaseConfig, 'cors'>,
 ): Type<CanActivate> {
-  @Injectable()
+  // Applied programmatically rather than as an `@Injectable()` decorator:
+  // the build tool (tsdown/oxc) does not lower legacy `experimentalDecorators`,
+  // so decorator syntax here would ship verbatim to `dist` and fail to parse
+  // under plain Node (CJS/ESM) at load time. Calling the decorator factory on
+  // the class produces identical DI metadata. See issue #87.
   class SupabaseAuthGuard implements CanActivate {
     async canActivate(executionContext: ExecutionContext): Promise<boolean> {
       // Fail loudly on non-HTTP transports rather than silently allowing them
@@ -123,5 +127,6 @@ export function withSupabase(
     }
   }
 
+  Injectable()(SupabaseAuthGuard)
   return SupabaseAuthGuard
 }