diff --git a/doc/api/zlib.md b/doc/api/zlib.md
index a791cbc7387ded..abc046fab4da76 100644
--- a/doc/api/zlib.md
+++ b/doc/api/zlib.md
@@ -115,7 +115,7 @@ const fs = require('fs');
 http.createServer((request, response) => {
   const raw = fs.createReadStream('index.html');
   // Store both a compressed and an uncompressed version of the resource.
-  response.setHeader('Vary: Accept-Encoding');
+  response.setHeader('Vary', 'Accept-Encoding');
   let acceptEncoding = request.headers['accept-encoding'];
   if (!acceptEncoding) {
     acceptEncoding = '';