diff --git a/example/shirtsize.go b/example/shirtsize.go
index e0bfc26..58bb247 100644
--- a/example/shirtsize.go
+++ b/example/shirtsize.go
@@ -6,8 +6,10 @@ package main
 
 import (
 	"encoding/json"
+	"fmt"
 	"log"
 	"os"
+	"strings"
 )
 
 //go:generate jsonenums -type=ShirtSize
@@ -37,6 +39,27 @@ const (
 	Sunday
 )
 
+func (d WeekDay) String() string {
+	switch d {
+	case Monday:
+		return "Dilluns"
+	case Tuesday:
+		return "Dimarts"
+	case Wednesday:
+		return "Dimecres"
+	case Thursday:
+		return "Dijous"
+	case Friday:
+		return "Divendres"
+	case Saturday:
+		return "Dissabte"
+	case Sunday:
+		return "Diumenge"
+	default:
+		return "invalid WeekDay"
+	}
+}
+
 func main() {
 	v := struct {
 		Size ShirtSize
@@ -45,4 +68,10 @@ func main() {
 	if err := json.NewEncoder(os.Stdout).Encode(v); err != nil {
 		log.Fatal(err)
 	}
+
+	input := `{"Size":"XL", "Day":"Dimarts"}`
+	if err := json.NewDecoder(strings.NewReader(input)).Decode(&v); err != nil {
+		log.Fatal(err)
+	}
+	fmt.Printf("decoded %s as %+v\n", input, v)
 }
diff --git a/example/shirtsize_jsonenums.go b/example/shirtsize_jsonenums.go
index 65ac8ad..41938cb 100644
--- a/example/shirtsize_jsonenums.go
+++ b/example/shirtsize_jsonenums.go
@@ -7,15 +7,13 @@ import (
 	"fmt"
 )
 
-var _ShirtSizeValueToName = map[ShirtSize]string{
-	NA: "NA", XS: "XS", S: "S", M: "M", L: "L", XL: "XL",
-}
-
 func (r ShirtSize) MarshalJSON() ([]byte, error) {
-	if s, ok := r.(fmt.Stringer); ok {
+	if s, ok := interface{}(r).(fmt.Stringer); ok {
 		return json.Marshal(s.String())
 	}
-	s, ok := _ShirtSizeValueToName[r]
+	s, ok := map[ShirtSize]string{
+		NA: "NA", XS: "XS", S: "S", M: "M", L: "L", XL: "XL",
+	}[r]
 	if !ok {
 		return nil, fmt.Errorf("invalid ShirtSize: %d", r)
 	}
@@ -26,6 +24,15 @@ var _ShirtSizeNameToValue = map[string]ShirtSize{
 	"NA": NA, "XS": XS, "S": S, "M": M, "L": L, "XL": XL,
 }
 
+func init() {
+	var v ShirtSize
+	if _, ok := interface{}(v).(fmt.Stringer); ok {
+		_ShirtSizeNameToValue = map[string]ShirtSize{
+			interface{}(NA).(fmt.Stringer).String(): NA, interface{}(XS).(fmt.Stringer).String(): XS, interface{}(S).(fmt.Stringer).String(): S, interface{}(M).(fmt.Stringer).String(): M, interface{}(L).(fmt.Stringer).String(): L, interface{}(XL).(fmt.Stringer).String(): XL,
+		}
+	}
+}
+
 func (r *ShirtSize) UnmarshalJSON(data []byte) error {
 	var s string
 	if err := json.Unmarshal(data, &s); err != nil {
diff --git a/example/weekday_jsonenums.go b/example/weekday_jsonenums.go
index 5e6f0b5..a58aa14 100644
--- a/example/weekday_jsonenums.go
+++ b/example/weekday_jsonenums.go
@@ -7,15 +7,13 @@ import (
 	"fmt"
 )
 
-var _WeekDayValueToName = map[WeekDay]string{
-	Monday: "Monday", Tuesday: "Tuesday", Wednesday: "Wednesday", Thursday: "Thursday", Friday: "Friday", Saturday: "Saturday", Sunday: "Sunday",
-}
-
 func (r WeekDay) MarshalJSON() ([]byte, error) {
-	if s, ok := r.(fmt.Stringer); ok {
+	if s, ok := interface{}(r).(fmt.Stringer); ok {
 		return json.Marshal(s.String())
 	}
-	s, ok := _WeekDayValueToName[r]
+	s, ok := map[WeekDay]string{
+		Monday: "Monday", Tuesday: "Tuesday", Wednesday: "Wednesday", Thursday: "Thursday", Friday: "Friday", Saturday: "Saturday", Sunday: "Sunday",
+	}[r]
 	if !ok {
 		return nil, fmt.Errorf("invalid WeekDay: %d", r)
 	}
@@ -26,6 +24,15 @@ var _WeekDayNameToValue = map[string]WeekDay{
 	"Monday": Monday, "Tuesday": Tuesday, "Wednesday": Wednesday, "Thursday": Thursday, "Friday": Friday, "Saturday": Saturday, "Sunday": Sunday,
 }
 
+func init() {
+	var v WeekDay
+	if _, ok := interface{}(v).(fmt.Stringer); ok {
+		_WeekDayNameToValue = map[string]WeekDay{
+			interface{}(Monday).(fmt.Stringer).String(): Monday, interface{}(Tuesday).(fmt.Stringer).String(): Tuesday, interface{}(Wednesday).(fmt.Stringer).String(): Wednesday, interface{}(Thursday).(fmt.Stringer).String(): Thursday, interface{}(Friday).(fmt.Stringer).String(): Friday, interface{}(Saturday).(fmt.Stringer).String(): Saturday, interface{}(Sunday).(fmt.Stringer).String(): Sunday,
+		}
+	}
+}
+
 func (r *WeekDay) UnmarshalJSON(data []byte) error {
 	var s string
 	if err := json.Unmarshal(data, &s); err != nil {
diff --git a/jsonenums.go b/jsonenums.go
index 7585a51..53798c2 100644
--- a/jsonenums.go
+++ b/jsonenums.go
@@ -154,8 +154,7 @@ type Package struct {
 	name  string
 	files []*ast.File
 
-	defs  map[*ast.Ident]types.Object
-	types *types.Package
+	defs map[*ast.Ident]types.Object
 }
 
 // parsePackage parses the package in the given directory and returns it.
@@ -188,8 +187,7 @@ func parsePackage(directory string, skipSuffix string) (*Package, error) {
 	defs := make(map[*ast.Ident]types.Object)
 	config := types.Config{FakeImportC: true}
 	info := &types.Info{Defs: defs}
-	types, err := config.Check(directory, fs, files, info)
-	if err != nil {
+	if _, err := config.Check(directory, fs, files, info); err != nil {
 		return nil, fmt.Errorf("type-checking package: %v", err)
 	}
 
@@ -197,7 +195,6 @@ func parsePackage(directory string, skipSuffix string) (*Package, error) {
 		name:  files[0].Name.Name,
 		files: files,
 		defs:  defs,
-		types: types,
 	}, nil
 }
 
diff --git a/template.go b/template.go
index e2ca209..dd78689 100644
--- a/template.go
+++ b/template.go
@@ -19,15 +19,14 @@ import (
 )
 
 {{range $typename, $values := .TypesAndValues}}
-var _{{$typename}}ValueToName = map[{{$typename}}]string {
-    {{range $values}}{{.}}: "{{.}}",{{end}}
-}
 
 func (r {{$typename}}) MarshalJSON() ([]byte, error) {
-    if s, ok := r.(fmt.Stringer); ok {
+    if s, ok := interface{}(r).(fmt.Stringer); ok {
         return json.Marshal(s.String())
     }
-    s, ok := _{{$typename}}ValueToName[r]
+    s, ok := map[{{$typename}}]string {
+        {{range $values}}{{.}}: "{{.}}",{{end}}
+    }[r]
     if !ok {
         return nil, fmt.Errorf("invalid {{$typename}}: %d", r)
     }
@@ -38,6 +37,15 @@ var _{{$typename}}NameToValue = map[string]{{$typename}} {
     {{range $values}}"{{.}}": {{.}},{{end}}
 }
 
+func init() {
+    var v {{$typename}}
+    if _, ok := interface{}(v).(fmt.Stringer); ok {
+        _{{$typename}}NameToValue = map[string]{{$typename}} {
+            {{range $values}}interface{}({{.}}).(fmt.Stringer).String(): {{.}},{{end}}
+        }
+    }
+}
+
 func (r *{{$typename}}) UnmarshalJSON(data []byte) error {
     var s string
     if err := json.Unmarshal(data, &s); err != nil {