diff --git a/config.md b/config.md
index a24130f8b..f8d2d904c 100644
--- a/config.md
+++ b/config.md
@@ -292,7 +292,7 @@ For Windows based systems the user structure has the following fields:
   This SHOULD only be set if **`platform.os`** is `linux`.
 * **`solaris`** (object, OPTIONAL) [Solaris-specific configuration](config-solaris.md).
   This SHOULD only be set if **`platform.os`** is `solaris`.
-* **`windows`** (object, optional) [Windows-specific configuration](config-windows.md).
+* **`windows`** (object, OPTIONAL) [Windows-specific configuration](config-windows.md).
   This SHOULD only be set if **`platform.os`** is `windows`.
 
 ### Example (Linux)