diff --git a/docs/docs/add-offline-support-with-a-service-worker.md b/docs/docs/add-offline-support-with-a-service-worker.md
index eb7438ff92231..d441fb10314f0 100644
--- a/docs/docs/add-offline-support-with-a-service-worker.md
+++ b/docs/docs/add-offline-support-with-a-service-worker.md
@@ -41,6 +41,8 @@ Add this plugin to your `gatsby-config.js`
 
 That's all you need to add offline support to your Gatsby site.
 
+Note: Service worker registers only in production builds (`gatsby build`).
+
 ## References
 
 - [Service Workers: an Introduction](https://developers.google.com/web/fundamentals/primers/service-workers/)