diff --git a/doc/api/process.md b/doc/api/process.md
index c973d15e12cef7..fdea86bf2d9039 100644
--- a/doc/api/process.md
+++ b/doc/api/process.md
@@ -84,7 +84,8 @@ process.on('exit', (code) => {
 added: v0.5.10
 -->
 
-* `message` {Object} a parsed JSON object or primitive value.
+* `message` { Object | boolean | number | string | null } a parsed JSON object
+  or a serializable primitive value.
 * `sendHandle` {net.Server|net.Socket} a [`net.Server`][] or [`net.Socket`][]
   object, or undefined.