diff --git a/src/display.rs b/src/display.rs
index a3754ed9..0bbc407c 100644
--- a/src/display.rs
+++ b/src/display.rs
@@ -8,7 +8,7 @@ impl Display for Date {
             // like `2015-11-02`
             Date::YMD { year, month, day } => write!(f, "{:04}-{:02}-{:02}", year, month, day),
             // like `2015-W45-01`
-            Date::Week { year, ww, d } => write!(f, "{:04}-{:02}-{:02}", year, ww, d),
+            Date::Week { year, ww, d } => write!(f, "{:04}-W{:02}-{:01}", year, ww, d),
             // like `2015-306`
             Date::Ordinal { year, ddd } => write!(f, "{:04}-{:03}", year, ddd),
         }
diff --git a/src/parsers/tests.rs b/src/parsers/tests.rs
index 4dc2362c..ff64f379 100644
--- a/src/parsers/tests.rs
+++ b/src/parsers/tests.rs
@@ -116,6 +116,10 @@ fn test_date_ordinal_date() {
 
 #[test]
 fn format_equivalence() {
+    assert_eq!(
+        parse_datetime(b"2001-02-03T04:05:06+07:00.001"),
+        parse_datetime(b"20010203T040506+0700.001")
+    );
     assert_eq!(
         parse_datetime(b"2001-02-03T04:05:06+07:00"),
         parse_datetime(b"20010203T040506+0700")
@@ -156,6 +160,49 @@ fn test_datetime_error() {
     }
 }
 
+#[rustfmt::skip]
+#[test]
+fn datetime_roundtrip_ymd() {
+    assert_parser!(
+        parse_datetime, "2001-02-03T04:05:06.000+07:00",
+        DateTime{
+            date: Date::YMD{year: 2001, month: 2, day: 3},
+            time: Time { hour: 4, minute: 5, second: 6, millisecond: 0, tz_offset_hours: 7, tz_offset_minutes: 0 }
+        }
+    );
+    assert_parser!(
+        parse_datetime, "2001-02-03T04:05:06.001+07:00",
+        DateTime{
+            date: Date::YMD{year: 2001, month: 2, day: 3},
+            time: Time { hour: 4, minute: 5, second: 6, millisecond: 1, tz_offset_hours: 7, tz_offset_minutes: 0 }
+        }
+    );
+}
+
+#[rustfmt::skip]
+#[test]
+fn datetime_roundtrip_week() {
+    assert_parser!(
+        parse_datetime, "2015-W05-6T04:05:06.001+07:00",
+        DateTime{
+            date: Date::Week { year: 2015, ww: 5, d: 6 },
+            time: Time { hour: 4, minute: 5, second: 6, millisecond: 1, tz_offset_hours: 7, tz_offset_minutes: 0 }
+        }
+    );
+}
+
+#[rustfmt::skip]
+#[test]
+fn datetime_roundtrip_ordinal() {
+    assert_parser!(
+        parse_datetime, "2001-035T04:05:06.001+07:00",
+        DateTime{
+            date: Date::Ordinal { year: 2001, ddd: 35 },
+            time: Time { hour: 4, minute: 5, second: 6, millisecond: 1, tz_offset_hours: 7, tz_offset_minutes: 0 }
+        }
+    );
+}
+
 #[test]
 fn disallows_notallowed() {
     assert!(parse_time(b"30:90:90").is_err());
@@ -287,13 +334,13 @@ fn test_duration_datetime_error() {
 #[test]
 fn test_duration_second_and_millisecond2() {
     assert_parser!(
-        parse_duration, "PT30S", 
+        parse_duration, "PT30S",
         Duration::YMDHMS { year: 0, month: 0, day: 0, hour: 0, minute: 0, second: 30, millisecond: 0 }
 
     );
 
     assert_parser!(
-        parse_duration, "PT30.123S", 
+        parse_duration, "PT30.123S",
         Duration::YMDHMS { year: 0, month: 0, day: 0, hour: 0, minute: 0, second: 30, millisecond: 123 }
 
     );
@@ -339,6 +386,14 @@ fn duration_roundtrip() {
         parse_duration, "P2021Y11M16DT0.471S",
         Duration::YMDHMS { year: 2021, month: 11, day: 16, hour: 0, minute: 0, second: 0, millisecond: 471 }
     );
+    assert_parser!(
+        parse_duration, "P2021Y11M16DT0.042S",
+        Duration::YMDHMS { year: 2021, month: 11, day: 16, hour: 0, minute: 0, second: 0, millisecond: 42 }
+    );
+    assert_parser!(
+        parse_duration, "P2021Y11M16DT0.004S",
+        Duration::YMDHMS { year: 2021, month: 11, day: 16, hour: 0, minute: 0, second: 0, millisecond: 4 }
+    );
     assert_parser!(
         parse_duration, "P2021Y11M",
         Duration::YMDHMS { year: 2021, month: 11, day: 0, hour: 0, minute: 0, second: 0, millisecond: 0 }
diff --git a/tests/lib.rs b/tests/lib.rs
index 1578be70..469fc841 100644
--- a/tests/lib.rs
+++ b/tests/lib.rs
@@ -38,6 +38,28 @@ fn test_millisecond() {
         );
         i += 1;
     }
+    assert_eq!(
+        Ok(Time {
+            hour: 16,
+            minute: 43,
+            second: 0,
+            millisecond: 42,
+            tz_offset_hours: 0,
+            tz_offset_minutes: 0
+        }),
+        time("16:43:00.042")
+    );
+    assert_eq!(
+        Ok(Time {
+            hour: 16,
+            minute: 43,
+            second: 0,
+            millisecond: 10,
+            tz_offset_hours: 0,
+            tz_offset_minutes: 0
+        }),
+        time("16:43:00.01")
+    );
     assert_eq!(
         Ok(Time {
             hour: 16,