diff --git a/CHANGELOG.md b/CHANGELOG.md
index b5afdf8..710107f 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,19 @@
 # Changelog
 
+## 0.4.0
+
+This is a full rewrite of the core implementation.
+
+* Allow negative values for semaphores.
+* Allow weights for `semaphore.acquire` and `semaphore.runExclusive`.
+  A waiter will be dispatched once the value of the semaphore is greater or
+  equal to its weight.
+* Add `semaphore.getValue` and `semaphore.setValue`.
+* Allow weights for `semaphore.waitForUnlock`. The promise will only resolve
+  once the value of the semaphore is greater or equal to its weight.
+* Only resolve `waitForUnlock` once no waiters remain (fixes #52).
+* `waitForUnlock` times out if the `withTimeout` decorator is used.
+
 ## 0.3.2
 
 * Add `waitForUnlock` for waiting until a mutex/semaphore is free for locking,
diff --git a/README.md b/README.md
index 79c3ecd..c0d35ea 100644
--- a/README.md
+++ b/README.md
@@ -155,7 +155,8 @@ try {
 
 `acquire` returns an (ES6) promise that will resolve as soon as the mutex is
 available. The promise resolves with a function `release` that
-must be called once the mutex should be released again.
+must be called once the mutex should be released again. The `release` callback
+is idempotent.
 
 **IMPORTANT:** Failure to call `release` will hold the mutex locked and will
 likely deadlock the application. Make sure to call `release` under all circumstances
@@ -321,7 +322,7 @@ try {
 available. The promise resolves to an array with the
 first entry being the current value of the semaphore, and the second value a
 function that must be called to release the semaphore once the critical operation
-has completed.
+has completed. The `release` callback is idempotent.
 
 **IMPORTANT:** Failure to call `release` will hold the semaphore locked and will
 likely deadlock the application. Make sure to call `release` under all circumstances