diff --git a/CHANGELOG.md b/CHANGELOG.md
index 5112703..7ff032c 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -13,6 +13,11 @@
 
 **Fixes**:
 
+- [#259](https://github.com/alecthomas/voluptuous/issues/259):
+  Fixed a performance issue of exponential complexity where all of the dict keys were matched against all keys in the schema.
+  This resulted in O(n*m) complexity where n is the number of keys in the dict being validated and m is the number of keys in the schema.
+  The fix ensures that each key in the dict is matched against the relevant schema keys only. It now works in O(n).
+
 ## 0.9.3 (2016-08-03)
 
 Changelog not kept for 0.9.3 and earlier releases.