diff --git a/model/time.go b/model/time.go
index 7b0064fd..490a0240 100644
--- a/model/time.go
+++ b/model/time.go
@@ -186,6 +186,10 @@ var durationRE = regexp.MustCompile("^([0-9]+)(y|w|d|h|m|s|ms)$")
 // ParseDuration parses a string into a time.Duration, assuming that a year
 // always has 365d, a week always has 7d, and a day always has 24h.
 func ParseDuration(durationStr string) (Duration, error) {
+	// Allow 0 without a unit.
+	if durationStr == "0" {
+		return 0, nil
+	}
 	matches := durationRE.FindStringSubmatch(durationStr)
 	if len(matches) != 3 {
 		return 0, fmt.Errorf("not a valid duration string: %q", durationStr)
diff --git a/model/time_test.go b/model/time_test.go
index 315bc4e5..330cc6e4 100644
--- a/model/time_test.go
+++ b/model/time_test.go
@@ -90,8 +90,14 @@ func TestParseDuration(t *testing.T) {
 	var cases = []struct {
 		in  string
 		out time.Duration
+
+		expectedString string
 	}{
 		{
+			in:             "0",
+			out:            0,
+			expectedString: "0s",
+		}, {
 			in:  "0s",
 			out: 0,
 		}, {
@@ -126,7 +132,11 @@ func TestParseDuration(t *testing.T) {
 		if time.Duration(d) != c.out {
 			t.Errorf("Expected %v but got %v", c.out, d)
 		}
-		if d.String() != c.in {
+		expectedString := c.expectedString
+		if c.expectedString == "" {
+			expectedString = c.in
+		}
+		if d.String() != expectedString {
 			t.Errorf("Expected duration string %q but got %q", c.in, d.String())
 		}
 	}