diff --git a/reflect_map.go b/reflect_map.go
index 5829671..4e479c8 100644
--- a/reflect_map.go
+++ b/reflect_map.go
@@ -2,11 +2,12 @@ package jsoniter
 
 import (
 	"fmt"
-	"github.com/modern-go/reflect2"
 	"io"
 	"reflect"
 	"sort"
 	"unsafe"
+
+	"github.com/modern-go/reflect2"
 )
 
 func decoderOfMap(ctx *ctx, typ reflect2.Type) ValDecoder {
@@ -106,15 +107,17 @@ func encoderOfMapKey(ctx *ctx, typ reflect2.Type) ValEncoder {
 		}
 	}
 
-	if typ == textMarshalerType {
-		return &directTextMarshalerEncoder{
-			stringEncoder: ctx.EncoderOf(reflect2.TypeOf("")),
+	if typ.Kind() != reflect.String {
+		if typ == textMarshalerType {
+			return &directTextMarshalerEncoder{
+				stringEncoder: ctx.EncoderOf(reflect2.TypeOf("")),
+			}
 		}
-	}
-	if typ.Implements(textMarshalerType) {
-		return &textMarshalerEncoder{
-			valType:       typ,
-			stringEncoder: ctx.EncoderOf(reflect2.TypeOf("")),
+		if typ.Implements(textMarshalerType) {
+			return &textMarshalerEncoder{
+				valType:       typ,
+				stringEncoder: ctx.EncoderOf(reflect2.TypeOf("")),
+			}
 		}
 	}