diff --git a/feature_stream_string.go b/feature_stream_string.go
index 2856836..8655f93 100644
--- a/feature_stream_string.go
+++ b/feature_stream_string.go
@@ -286,9 +286,8 @@ func writeStringSlowPathWithHTMLEscaped(stream *Stream, i int, s string, valLen
 		}
 		c, size := utf8.DecodeRuneInString(s[i:])
 		if c == utf8.RuneError && size == 1 {
-			if start < i {
-				stream.WriteRaw(s[start:i])
-			}
+			i++
+			stream.WriteRaw(s[start:i])
 			start = i
 			continue
 		}
diff --git a/jsoniter_invalid_test.go b/jsoniter_invalid_test.go
index f328a16..ba864b4 100644
--- a/jsoniter_invalid_test.go
+++ b/jsoniter_invalid_test.go
@@ -5,6 +5,7 @@ import (
 	"github.com/stretchr/testify/require"
 	"io"
 	"testing"
+	"bytes"
 )
 
 func Test_missing_object_end(t *testing.T) {
@@ -113,3 +114,16 @@ func Test_chan(t *testing.T) {
 	should.Nil(err)
 	should.Equal(``, str)
 }
+
+func Test_invalid_number(t *testing.T) {
+	type Message struct {
+		Number int `json:"number"`
+	}
+	obj := Message{}
+	decoder := ConfigCompatibleWithStandardLibrary.NewDecoder(bytes.NewBufferString(`{"number":"5"}`))
+	err := decoder.Decode(&obj)
+	result, err := ConfigCompatibleWithStandardLibrary.Marshal(err.Error())
+	should := require.New(t)
+	should.Nil(err)
+	should.Contains(string(result), "\xff")
+}