diff --git a/feature_reflect.go b/feature_reflect.go
index 100e7e6..62fc892 100644
--- a/feature_reflect.go
+++ b/feature_reflect.go
@@ -5,6 +5,7 @@ import (
 	"reflect"
 	"sync/atomic"
 	"unsafe"
+	"errors"
 )
 
 /*
@@ -345,7 +346,11 @@ func decoderOfType(typ reflect.Type) (Decoder, error) {
 	case reflect.Bool:
 		return &boolCodec{}, nil
 	case reflect.Interface:
-		return &interfaceCodec{}, nil
+		if typ.NumMethod() == 0 {
+			return &interfaceCodec{}, nil
+		} else {
+			return nil, errors.New("unsupportd type: " + typ.String())
+		}
 	case reflect.Struct:
 		return prefix(fmt.Sprintf("[%s]", typeName)).addToDecoder(decoderOfStruct(typ))
 	case reflect.Slice:
diff --git a/jsoniter_interface_test.go b/jsoniter_interface_test.go
index 8dd8844..e1d78ba 100644
--- a/jsoniter_interface_test.go
+++ b/jsoniter_interface_test.go
@@ -3,6 +3,7 @@ package jsoniter
 import (
 	"testing"
 	"github.com/json-iterator/go/require"
+	"unsafe"
 )
 
 func Test_write_array_of_interface(t *testing.T) {
@@ -22,11 +23,20 @@ func Test_write_map_of_interface(t *testing.T) {
 }
 
 type MyInterface interface {
+	Hello() string
+}
+
+type MyString string
+
+func (ms MyString) Hello() string {
+	return string(ms)
 }
 
 func Test_write_map_of_custom_interface(t *testing.T) {
 	should := require.New(t)
-	val := map[string]MyInterface{"hello":"world"}
+	myStr := MyString("world")
+	should.Equal("world", myStr.Hello())
+	val := map[string]MyInterface{"hello":myStr}
 	str, err := MarshalToString(val)
 	should.Nil(err)
 	should.Equal(`{"hello":"world"}`, str)
@@ -39,4 +49,23 @@ func Test_write_interface(t *testing.T) {
 	str, err := MarshalToString(val)
 	should.Nil(err)
 	should.Equal(`"hello"`, str)
+}
+
+func Test_read_interface(t *testing.T) {
+	should := require.New(t)
+	var val interface{}
+	err := UnmarshalFromString(`"hello"`, &val)
+	should.Nil(err)
+	should.Equal("hello", val)
+}
+
+func Test_read_custom_interface(t *testing.T) {
+	should := require.New(t)
+	var val MyInterface
+	RegisterTypeDecoder("jsoniter.MyInterface", func(ptr unsafe.Pointer, iter *Iterator) {
+		*((*MyInterface)(ptr)) = MyString(iter.ReadString())
+	})
+	err := UnmarshalFromString(`"hello"`, &val)
+	should.Nil(err)
+	should.Equal("hello", val.Hello())
 }
\ No newline at end of file