diff --git a/pttodo/ts.go b/pttodo/ts.go
index 737a4c3..f33691d 100644
--- a/pttodo/ts.go
+++ b/pttodo/ts.go
@@ -8,10 +8,18 @@ import (
 type TS int64
 
 func (ts TS) MarshalJSON() ([]byte, error) {
+	v, err := ts.MarshalYAML()
+	if err != nil {
+		return nil, err
+	}
+	return json.Marshal(v)
+}
+
+func (ts TS) MarshalYAML() (interface{}, error) {
 	if ts == 0 {
 		ts = TS(time.Now().Unix())
 	}
-	return json.Marshal(int64(ts))
+	return int64(ts), nil
 }
 
 func (ts *TS) UnmarshalJSON(b []byte) error {