diff --git a/docs/api/ffi.md b/docs/api/ffi.md
index 6284689cb271b5..1256666923fd8d 100644
--- a/docs/api/ffi.md
+++ b/docs/api/ffi.md
@@ -280,6 +280,7 @@ const searchIterator = new JSCallback(
   {
     returns: "bool",
     args: ["ptr", "usize"],
+    threadsafe: true // Optional. Defaults to `false`
   },
 );