diff --git a/CHANGELOG.md b/CHANGELOG.md
index f27646d..5b87012 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -8,10 +8,32 @@ Chrono obeys the principle of [Semantic Versioning](http://semver.org/).
 There were/are numerous minor versions before 1.0 due to the language changes.
 Versions with only mechnical changes will be omitted from the following list.
 
+## 0.4.1
+
+### Bug Fixes
+
+* Allow parsing timestamps with subsecond precision (@jonasbb)
+* RFC2822 allows times to not include the second (@upsuper)
+
+### Features
+
+* New `timestamp_millis` method on `DateTime` and `NaiveDateTim` that returns
+  number of milliseconds since the epoch. (@quodlibetor)
+* Support exact decimal width on subsecond display for RFC3339 via a new
+  `to_rfc3339_opts` method on `DateTime` (@dekellum)
+* Use no_std-compatible num dependencies (@cuviper)
+* Add `SubsecRound` trait that allows rounding to the nearest second
+  (@dekellum)
+
+### Code Hygiene and Docs
+
+* Docs! (@alatiera @kosta @quodlibetor @kennytm)
+* Run clippy and various fixes (@quodlibetor)
+
 ## 0.4.0 (2017-06-22)
 
-This was originally planned as a minor release but was pushed to a major release
-due to the compatibility concern raised.
+This was originally planned as a minor release but was pushed to a major
+release due to the compatibility concern raised.
 
 ### Added
 
diff --git a/Cargo.toml b/Cargo.toml
index 713207b..731f11b 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -1,6 +1,6 @@
 [package]
 name = "chrono"
-version = "0.4.0"
+version = "0.4.1"
 authors = ["Kang Seonghoon <public+rust@mearie.org>"]
 
 description = "Date and time library for Rust"
diff --git a/src/datetime.rs b/src/datetime.rs
index 36fd160..ec5e85a 100644
--- a/src/datetime.rs
+++ b/src/datetime.rs
@@ -18,6 +18,8 @@ use format::{parse, Parsed, ParseError, ParseResult, DelayedFormat, StrftimeItem
 
 /// Specific formatting options for seconds. This may be extended in the
 /// future, so exhaustive matching in external code is not recommended.
+///
+/// See the `TimeZone::to_rfc3339_opts` function for usage.
 #[derive(Clone, Copy, Debug, Eq, PartialEq)]
 pub enum SecondsFormat {
     /// Format whole seconds only, with no decimal point nor subseconds.
@@ -39,6 +41,10 @@ pub enum SecondsFormat {
     /// display all available non-zero sub-second digits.  This corresponds to
     /// [Fixed::Nanosecond](format/enum.Fixed.html#variant.Nanosecond).
     AutoSi,
+
+    // Do not match against this.
+    #[doc(hidden)]
+    __NonExhaustive,
 }
 
 /// ISO 8601 combined date and time with time zone.
@@ -300,6 +306,8 @@ impl<Tz: TimeZone> DateTime<Tz> where Tz::Offset: fmt::Display {
         use format::Pad::Zero;
         use SecondsFormat::*;
 
+        debug_assert!(secform != __NonExhaustive, "Do not use __NonExhaustive!");
+
         const PREFIX: &'static [Item<'static>] = &[
             Item::Numeric(Year, Zero),
             Item::Literal("-"),
@@ -320,6 +328,7 @@ impl<Tz: TimeZone> DateTime<Tz> where Tz::Offset: fmt::Display {
             Micros => Some(Item::Fixed(Fixed::Nanosecond6)),
             Nanos  => Some(Item::Fixed(Fixed::Nanosecond9)),
             AutoSi => Some(Item::Fixed(Fixed::Nanosecond)),
+            __NonExhaustive => unreachable!(),
         };
 
         let tzitem = Item::Fixed(
@@ -1177,6 +1186,14 @@ mod tests {
         assert_eq!(ut.to_rfc3339_opts(AutoSi, true),  "2018-01-11T02:05:13.084660Z");
     }
 
+    #[test]
+    #[should_panic]
+    fn test_rfc3339_opts_nonexhaustive() {
+        use SecondsFormat;
+        let dt = Utc.ymd(1999, 10, 9).and_hms(1, 2, 3);
+        dt.to_rfc3339_opts(SecondsFormat::__NonExhaustive, true);
+    }
+
     #[test]
     fn test_datetime_from_str() {
         assert_eq!("2015-2-18T23:16:9.15Z".parse::<DateTime<FixedOffset>>(),