diff --git a/CHANGELOG.md b/CHANGELOG.md
index fe2c732..4bcf319 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,4 +1,5 @@
 ## v1.2.1 → v2.0.0
+  * **MIGRATION NOTE**: Please be sure to use `lein clean` to clear old (v1) build artifacts!
   * Refactored for huge performance improvements (~40% roundtrip time).
   * New header format for better error messages.
   * New `taoensso.nippy.tools` ns for easier integration with 3rd-party tools.
diff --git a/README.md b/README.md
index 2a7abad..5994fdc 100644
--- a/README.md
+++ b/README.md
@@ -9,6 +9,8 @@ v2 adds pluggable compression, crypto support (also pluggable), an improved API
   * **BREAKING**: Nothing (but please test first).
   * **DEPRECATED**: `freeze-to-bytes`->`freeze`, `thaw-from-bytes`->`thaw`.
 
+**Migration note**: Please be sure to use `lein clean` to clear old (v1) build artifacts!
+
 # Nippy, a Clojure serialization library
 
 Clojure's [rich data types](http://clojure.org/datatypes) are *awesome*. And its [reader](http://clojure.org/reader) allows you to take your data just about anywhere. But the reader can be painfully slow when you've got a lot of data to crunch (like when you're serializing to a database).