diff --git a/CHANGELOG.md b/CHANGELOG.md
index e6eed61..69c70b6 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -6,6 +6,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [unreleased]
 
+## [0.4.0] - 2021-09-14
+
 ### Changed
 
  - Use a variation of the [X-Macro] pattern instead of `iFn`. This change makes the implementation easier to reason about [**BC**].
diff --git a/interface99.h b/interface99.h
index 7d94774..0c6e93a 100644
--- a/interface99.h
+++ b/interface99.h
@@ -71,7 +71,7 @@ SOFTWARE.
 #define VTABLE99(implementor, iface) ML99_CAT4(implementor, _, iface, _impl)
 
 #define IFACE99_MAJOR 0
-#define IFACE99_MINOR 3
+#define IFACE99_MINOR 4
 #define IFACE99_PATCH 0
 // } (Public stuff)