diff --git a/common/bytes.go b/common/bytes.go
index 1ec880c2..ba81bbe9 100644
--- a/common/bytes.go
+++ b/common/bytes.go
@@ -26,7 +26,7 @@ func (bz HexBytes) MarshalJSON() ([]byte, error) {
 	jbz := make([]byte, len(s)+2)
 	jbz[0] = '"'
 	copy(jbz[1:], []byte(s))
-	jbz[1] = '"'
+	jbz[len(jbz)-1] = '"'
 	return jbz, nil
 }
 
diff --git a/common/bytes_test.go b/common/bytes_test.go
index 3e693b23..9e11988f 100644
--- a/common/bytes_test.go
+++ b/common/bytes_test.go
@@ -35,8 +35,8 @@ func TestJSONMarshal(t *testing.T) {
 		expected string
 	}{
 		{[]byte(``), `{"B1":"","B2":""}`},
-		{[]byte(``), `{"B1":"","B2":""}`},
-		{[]byte(``), `{"B1":"","B2":""}`},
+		{[]byte(`a`), `{"B1":"YQ==","B2":"61"}`},
+		{[]byte(`abc`), `{"B1":"YWJj","B2":"616263"}`},
 	}
 
 	for i, tc := range cases {