diff --git a/CHANGELOG.md b/CHANGELOG.md
index 00857b3..ccf6aee 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,8 @@
 # Unreleased
 
+# 4.0.0
+
+* Update html5ever to 0.27
 * feature: change lifetimes on UrlRelative (breaking change)
 * chore: use the `Display` trait (and `ToString`) instead of an inherent `to_string` method (breaking change)
 
diff --git a/Cargo.toml b/Cargo.toml
index 4ba171a..08daa1e 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -1,6 +1,6 @@
 [package]
 name = "ammonia"
-version = "3.3.0"
+version = "4.0.0"
 authors = ["Michael Howell <michael@notriddle.com>"]
 description = "HTML Sanitization"
 keywords = [ "sanitization", "html", "security", "xss" ]
diff --git a/README.md b/README.md
index c773dbb..ea32107 100644
--- a/README.md
+++ b/README.md
@@ -26,7 +26,7 @@ To use `ammonia`, add it to your project's `Cargo.toml` file:
 
 ```toml
 [dependencies]
-ammonia = "3"
+ammonia = "4"
 ```