diff --git a/opt/gotemplate_Bool.go b/opt/gotemplate_Bool.go
index 26f076b..89e6132 100644
--- a/opt/gotemplate_Bool.go
+++ b/opt/gotemplate_Bool.go
@@ -1,3 +1,5 @@
+// generated by gotemplate
+
 package opt
 
 import (
diff --git a/opt/gotemplate_Float32.go b/opt/gotemplate_Float32.go
index 82056ba..93ade1c 100644
--- a/opt/gotemplate_Float32.go
+++ b/opt/gotemplate_Float32.go
@@ -1,3 +1,5 @@
+// generated by gotemplate
+
 package opt
 
 import (
diff --git a/opt/gotemplate_Float64.go b/opt/gotemplate_Float64.go
index 269a254..90af91b 100644
--- a/opt/gotemplate_Float64.go
+++ b/opt/gotemplate_Float64.go
@@ -1,3 +1,5 @@
+// generated by gotemplate
+
 package opt
 
 import (
diff --git a/opt/gotemplate_Int.go b/opt/gotemplate_Int.go
index 62c75ed..71e74e8 100644
--- a/opt/gotemplate_Int.go
+++ b/opt/gotemplate_Int.go
@@ -1,3 +1,5 @@
+// generated by gotemplate
+
 package opt
 
 import (
diff --git a/opt/gotemplate_Int16.go b/opt/gotemplate_Int16.go
index 44a96f3..987e3df 100644
--- a/opt/gotemplate_Int16.go
+++ b/opt/gotemplate_Int16.go
@@ -1,3 +1,5 @@
+// generated by gotemplate
+
 package opt
 
 import (
diff --git a/opt/gotemplate_Int32.go b/opt/gotemplate_Int32.go
index 305fedb..e5f30d8 100644
--- a/opt/gotemplate_Int32.go
+++ b/opt/gotemplate_Int32.go
@@ -1,3 +1,5 @@
+// generated by gotemplate
+
 package opt
 
 import (
diff --git a/opt/gotemplate_Int64.go b/opt/gotemplate_Int64.go
index c3402ad..ff67a33 100644
--- a/opt/gotemplate_Int64.go
+++ b/opt/gotemplate_Int64.go
@@ -1,3 +1,5 @@
+// generated by gotemplate
+
 package opt
 
 import (
diff --git a/opt/gotemplate_Int8.go b/opt/gotemplate_Int8.go
index 3c8a6e4..41312d1 100644
--- a/opt/gotemplate_Int8.go
+++ b/opt/gotemplate_Int8.go
@@ -1,3 +1,5 @@
+// generated by gotemplate
+
 package opt
 
 import (
diff --git a/opt/gotemplate_String.go b/opt/gotemplate_String.go
index b9bba45..3d818fa 100644
--- a/opt/gotemplate_String.go
+++ b/opt/gotemplate_String.go
@@ -1,3 +1,5 @@
+// generated by gotemplate
+
 package opt
 
 import (
diff --git a/opt/gotemplate_Uint.go b/opt/gotemplate_Uint.go
index af71b9b..367db67 100644
--- a/opt/gotemplate_Uint.go
+++ b/opt/gotemplate_Uint.go
@@ -1,3 +1,5 @@
+// generated by gotemplate
+
 package opt
 
 import (
diff --git a/opt/gotemplate_Uint16.go b/opt/gotemplate_Uint16.go
index e47f62b..6abc71d 100644
--- a/opt/gotemplate_Uint16.go
+++ b/opt/gotemplate_Uint16.go
@@ -1,3 +1,5 @@
+// generated by gotemplate
+
 package opt
 
 import (
diff --git a/opt/gotemplate_Uint32.go b/opt/gotemplate_Uint32.go
index 286c99a..490945c 100644
--- a/opt/gotemplate_Uint32.go
+++ b/opt/gotemplate_Uint32.go
@@ -1,3 +1,5 @@
+// generated by gotemplate
+
 package opt
 
 import (
diff --git a/opt/gotemplate_Uint64.go b/opt/gotemplate_Uint64.go
index 2ec9237..37d2d41 100644
--- a/opt/gotemplate_Uint64.go
+++ b/opt/gotemplate_Uint64.go
@@ -1,3 +1,5 @@
+// generated by gotemplate
+
 package opt
 
 import (
diff --git a/opt/gotemplate_Uint8.go b/opt/gotemplate_Uint8.go
index 8306a97..55c4cdb 100644
--- a/opt/gotemplate_Uint8.go
+++ b/opt/gotemplate_Uint8.go
@@ -1,3 +1,5 @@
+// generated by gotemplate
+
 package opt
 
 import (
diff --git a/opt/optional/opt.go b/opt/optional/opt.go
index d828b97..6d3a079 100644
--- a/opt/optional/opt.go
+++ b/opt/optional/opt.go
@@ -1,3 +1,5 @@
+// +build none
+
 package optional
 
 import (
diff --git a/opt/opts.go b/opt/opts.go
index 7f81f6f..3617f7f 100644
--- a/opt/opts.go
+++ b/opt/opts.go
@@ -1,5 +1,6 @@
 package opt
 
+//go:generate sed -i "s/\\+build none/generated by gotemplate/" optional/opt.go
 //go:generate gotemplate "github.com/mailru/easyjson/opt/optional" Int(int)
 //go:generate gotemplate "github.com/mailru/easyjson/opt/optional" Uint(uint)
 
@@ -18,3 +19,4 @@ package opt
 
 //go:generate gotemplate "github.com/mailru/easyjson/opt/optional" Bool(bool)
 //go:generate gotemplate "github.com/mailru/easyjson/opt/optional" String(string)
+//go:generate sed -i "s/generated by gotemplate/+build none/" optional/opt.go
diff --git a/tests/basic_test.go b/tests/basic_test.go
index 5115668..9c97614 100644
--- a/tests/basic_test.go
+++ b/tests/basic_test.go
@@ -3,8 +3,28 @@ package tests
 import (
 	"reflect"
 	"testing"
+
+	"encoding/json"
 )
 
+type testType interface {
+	json.Marshaler
+	json.Unmarshaler
+}
+
+var testCases = []struct {
+	Decoded testType
+	Encoded string
+}{
+	{&primitiveTypesValue, primitiveTypesString},
+	{&structsValue, structsString},
+	{&omitEmptyValue, omitEmptyString},
+	{&snakeStructValue, snakeStructString},
+	{&omitEmptyDefaultValue, omitEmptyDefaultString},
+	{&optsValue, optsString},
+	{&rawValue, rawString},
+}
+
 func TestMarshal(t *testing.T) {
 	for i, test := range testCases {
 		data, err := test.Decoded.MarshalJSON()
diff --git a/tests/data.go b/tests/data.go
index bc57e00..806e4e3 100644
--- a/tests/data.go
+++ b/tests/data.go
@@ -1,7 +1,6 @@
 package tests
 
 import (
-	"encoding/json"
 	"fmt"
 	"math"
 
@@ -9,24 +8,6 @@ import (
 	"github.com/mailru/easyjson/opt"
 )
 
-type testType interface {
-	json.Marshaler
-	json.Unmarshaler
-}
-
-var testCases = []struct {
-	Decoded testType
-	Encoded string
-}{
-	{&primitiveTypesValue, primitiveTypesString},
-	{&structsValue, structsString},
-	{&omitEmptyValue, omitEmptyString},
-	{&snakeStructValue, snakeStructString},
-	{&omitEmptyDefaultValue, omitEmptyDefaultString},
-	{&optsValue, optsString},
-	{&rawValue, rawString},
-}
-
 type PrimitiveTypes struct {
 	String string
 	Bool   bool