diff --git a/README.md b/README.md
index 891b77ae..f7c622ed 100644
--- a/README.md
+++ b/README.md
@@ -95,6 +95,13 @@ func ExampleMarshal() {
 }
 ```
 
+### Struct fields
+
+Only exported struct fields are encoded and decoded. Unexported fields (those
+whose names start with a lowercase letter) are ignored, matching the behavior
+of Go's `encoding/json` package. Use an exported field, or a custom encoder,
+when a value needs to be included in the MessagePack representation.
+
 ## Contributors
 
 Thanks to all the people who already contributed!