diff -r bacb4ed5791c src/pkg/json/decode.go
--- a/src/pkg/json/decode.go	Thu Aug 04 16:38:18 2011 +1000
+++ b/src/pkg/json/decode.go	Mon Aug 22 16:54:45 2011 +1000
@@ -549,6 +549,17 @@
 	item := d.data[start:d.off]
 
 	// Check for unmarshaler.
+	// first, check if we can do an immediate unmarshalling.
+	if v.CanAddr() {
+		unmarshaler, ok := v.Addr().Interface().(Unmarshaler)
+		if ok {
+			err := unmarshaler.UnmarshalJSON(item)
+			if err != nil {
+				d.error(err)
+			}
+			return
+		}
+	}
 	wantptr := item[0] == 'n' // null
 	unmarshaler, pv := d.indirect(v, wantptr)
 	if unmarshaler != nil {