diff --git a/db.go b/db.go
index 16a34d6..3aaa7c6 100644
--- a/db.go
+++ b/db.go
@@ -1,9 +1,6 @@
 package main
 
 import (
-	"errors"
-	"fmt"
-	"strconv"
 	"time"
 
 	"github.com/google/uuid"
@@ -22,7 +19,6 @@ type (
 	user struct {
 		History map[string][]History
 	}
-	duration time.Duration
 )
 
 func (db db) HistoryOf(user string) map[string][]History {
@@ -88,57 +84,3 @@ func (db db) lastTS(user, q string) time.Time {
 	}
 	return time.Unix(0, max)
 }
-
-func (d duration) MarshalYAML() (interface{}, error) {
-	return d.String(), nil
-}
-
-func (d duration) String() string {
-	result := ""
-	if weeks := time.Duration(d) / (time.Hour * 24 * 7); weeks > 0 {
-		result += fmt.Sprintf("%dw", weeks)
-		d -= duration(weeks * time.Hour * 24 * 7)
-	}
-	if days := time.Duration(d) / (time.Hour * 24); days > 0 {
-		result += fmt.Sprintf("%dd", days)
-		d -= duration(days * time.Hour * 24)
-	}
-	return result + time.Duration(d).String()
-}
-
-func (d *duration) UnmarshalYAML(unmarshal func(interface{}) error) error {
-	var s string
-	if err := unmarshal(&s); err != nil {
-		return err
-	}
-	count := ""
-	var ttl time.Duration
-	for i := range s {
-		if s[i] < '0' || s[i] > '9' {
-			n, err := strconv.Atoi(count)
-			if err != nil {
-				return err
-			}
-			count += s[i : i+1]
-			switch s[i] {
-			case 'w':
-				count = fmt.Sprintf("%dh", n*24*7)
-			case 'd':
-				count = fmt.Sprintf("%dh", n*24)
-			}
-			d, err := time.ParseDuration(count)
-			if err != nil {
-				return err
-			}
-			ttl += d
-			count = ""
-		} else {
-			count += s[i : i+1]
-		}
-	}
-	if count != "" {
-		return errors.New(count)
-	}
-	*d = duration(ttl)
-	return nil
-}
diff --git a/duration.go b/duration.go
new file mode 100644
index 0000000..eb11283
--- /dev/null
+++ b/duration.go
@@ -0,0 +1,64 @@
+package main
+
+import (
+	"errors"
+	"fmt"
+	"strconv"
+	"time"
+)
+
+type duration time.Duration
+
+func (d duration) MarshalYAML() (interface{}, error) {
+	return d.String(), nil
+}
+
+func (d duration) String() string {
+	result := ""
+	if weeks := time.Duration(d) / (time.Hour * 24 * 7); weeks > 0 {
+		result += fmt.Sprintf("%dw", weeks)
+		d -= duration(weeks * time.Hour * 24 * 7)
+	}
+	if days := time.Duration(d) / (time.Hour * 24); days > 0 {
+		result += fmt.Sprintf("%dd", days)
+		d -= duration(days * time.Hour * 24)
+	}
+	return result + time.Duration(d).String()
+}
+
+func (d *duration) UnmarshalYAML(unmarshal func(interface{}) error) error {
+	var s string
+	if err := unmarshal(&s); err != nil {
+		return err
+	}
+	count := ""
+	var ttl time.Duration
+	for i := range s {
+		if s[i] < '0' || s[i] > '9' {
+			n, err := strconv.Atoi(count)
+			if err != nil {
+				return err
+			}
+			count += s[i : i+1]
+			switch s[i] {
+			case 'w':
+				count = fmt.Sprintf("%dh", n*24*7)
+			case 'd':
+				count = fmt.Sprintf("%dh", n*24)
+			}
+			d, err := time.ParseDuration(count)
+			if err != nil {
+				return err
+			}
+			ttl += d
+			count = ""
+		} else {
+			count += s[i : i+1]
+		}
+	}
+	if count != "" {
+		return errors.New(count)
+	}
+	*d = duration(ttl)
+	return nil
+}
diff --git a/duration_test.go b/duration_test.go
new file mode 100644
index 0000000..0010062
--- /dev/null
+++ b/duration_test.go
@@ -0,0 +1,38 @@
+package main
+
+import (
+	"testing"
+	"time"
+
+	"gopkg.in/yaml.v2"
+)
+
+func TestDurationYAML(t *testing.T) {
+	cases := map[string]time.Duration{
+		"":           0,
+		"1s":         time.Second,
+		"1m1s":       time.Minute + time.Second,
+		"1h1s":       time.Hour + time.Second,
+		"1d":         24 * time.Hour,
+		"1w":         7 * 24 * time.Hour,
+		"1w2d3h4m5s": 7*24*time.Hour + 2*24*time.Hour + 3*time.Hour + 4*time.Minute + 5*time.Second,
+	}
+
+	for name, wantd := range cases {
+		want := wantd
+		t.Run(name, func(t *testing.T) {
+			var d1, d2 duration
+			if err := yaml.Unmarshal([]byte(name), &d1); err != nil {
+				t.Error(err)
+			} else if time.Duration(d1) != want {
+				t.Error(d1)
+			} else if b, err := yaml.Marshal(d1); err != nil {
+				t.Error(err)
+			} else if err := yaml.Unmarshal(b, &d2); err != nil {
+				t.Error(err)
+			} else if d1 != d2 {
+				t.Error(d1, d2)
+			}
+		})
+	}
+}