diff --git a/CHANGELOG.md b/CHANGELOG.md
index 47e88b9..21d607c 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -2,6 +2,8 @@
 
 * New option `IgnoreUntaggedFields` to ignore decoding to any fields
   without `mapstructure` (or the configured tag name) set [GH-277]
+* New option `ErrorUnset` which makes it an error if any fields
+  in a target struct are not set by the decoding process. [GH-225]
 * Decoding to slice from array no longer crashes [GH-265]
 * Decode nested struct pointers to map [GH-271]
 * Fix issue where `,squash` was ignored if `Squash` option was set. [GH-280]
diff --git a/mapstructure.go b/mapstructure.go
index 995c84b..32c9fce 100644
--- a/mapstructure.go
+++ b/mapstructure.go
@@ -217,7 +217,8 @@ type DecoderConfig struct {
 
 	// If ErrorUnset is true, then it is an error for there to exist
 	// fields in the result that were not set in the decoding process
-	// (extra fields).
+	// (extra fields). This only applies to decoding to a struct. This
+	// will affect all nested structs as well.
 	ErrorUnset bool
 
 	// ZeroFields, if set to true, will zero fields before writing them.