diff --git a/template.go b/template.go
index dd78689..f937a6f 100644
--- a/template.go
+++ b/template.go
@@ -20,32 +20,39 @@ import (
 
 {{range $typename, $values := .TypesAndValues}}
 
-func (r {{$typename}}) MarshalJSON() ([]byte, error) {
-    if s, ok := interface{}(r).(fmt.Stringer); ok {
-        return json.Marshal(s.String())
+var (
+    _{{$typename}}NameToValue = map[string]{{$typename}} {
+        {{range $values}}"{{.}}": {{.}},
+        {{end}}
     }
-    s, ok := map[{{$typename}}]string {
-        {{range $values}}{{.}}: "{{.}}",{{end}}
-    }[r]
-    if !ok {
-        return nil, fmt.Errorf("invalid {{$typename}}: %d", r)
-    }
-    return json.Marshal(s)
-}
 
-var _{{$typename}}NameToValue = map[string]{{$typename}} {
-    {{range $values}}"{{.}}": {{.}},{{end}}
-}
+    _{{$typename}}ValueToName = map[{{$typename}}]string {
+        {{range $values}}{{.}}: "{{.}}",
+        {{end}}
+    }
+)
 
 func init() {
     var v {{$typename}}
     if _, ok := interface{}(v).(fmt.Stringer); ok {
         _{{$typename}}NameToValue = map[string]{{$typename}} {
-            {{range $values}}interface{}({{.}}).(fmt.Stringer).String(): {{.}},{{end}}
+            {{range $values}}interface{}({{.}}).(fmt.Stringer).String(): {{.}},
+            {{end}}
         }
     }
 }
 
+func (r {{$typename}}) MarshalJSON() ([]byte, error) {
+    if s, ok := interface{}(r).(fmt.Stringer); ok {
+        return json.Marshal(s.String())
+    }
+    s, ok := _{{$typename}}ValueToName[r]
+    if !ok {
+        return nil, fmt.Errorf("invalid {{$typename}}: %d", r)
+    }
+    return json.Marshal(s)
+}
+
 func (r *{{$typename}}) UnmarshalJSON(data []byte) error {
     var s string
     if err := json.Unmarshal(data, &s); err != nil {