diff --git a/errors.go b/errors.go
index 29c7bcd..0cf5ef0 100644
--- a/errors.go
+++ b/errors.go
@@ -49,6 +49,11 @@ func (e *JSONError) Error() string {
 }
 
 func NewJSONError(str []byte, pos int, msg string) *JSONError {
+	if pos < 0 {
+		pos = 0
+	} else if pos > len(str)-1 {
+		pos = len(str) - 1
+	}
 	sublen := 10
 	start := pos - sublen
 	end := pos + sublen
@@ -61,6 +66,6 @@ func NewJSONError(str []byte, pos int, msg string) *JSONError {
 	substr := make([]byte, end-start+1)
 	copy(substr, str[start:pos])
 	substr[pos-start] = '^'
-	copy(substr[pos-start+1:], str[pos+1:end])
+	copy(substr[pos-start+1:], str[pos:end])
 	return &JSONError{pos: pos, substr: string(substr), msg: msg}
 }
diff --git a/errors_test.go b/errors_test.go
new file mode 100644
index 0000000..8ee36b2
--- /dev/null
+++ b/errors_test.go
@@ -0,0 +1,57 @@
+// Copyright 2019 Yunion
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package jsonutils // import "yunion.io/x/jsonutils"
+
+import "testing"
+
+func TestNewJSONError(t *testing.T) {
+	cases := []struct {
+		str []byte
+		pos int
+	}{
+		{
+			str: []byte(`{"a":1,"b":2}`),
+			pos: 0,
+		},
+		{
+			str: []byte(`{"a":1,"b":2}`),
+			pos: 1,
+		},
+		{
+			str: []byte(`{"a":1,"b":2}`),
+			pos: 10,
+		},
+		{
+			str: []byte(`{"a":1,"b":2}`),
+			pos: 11,
+		},
+		{
+			str: []byte(`{"a":1,"b":2}`),
+			pos: 12,
+		},
+		{
+			str: []byte(`{"a":1,"b":2}`),
+			pos: 5,
+		},
+		{
+			str: []byte(`{"a":1,"b":2}`),
+			pos: 30,
+		},
+	}
+	for _, c := range cases {
+		err := NewJSONError(c.str, c.pos, "expected a number")
+		t.Logf("error: %v", err)
+	}
+}