diff --git a/README.md b/README.md
index e0e436c..642d46a 100644
--- a/README.md
+++ b/README.md
@@ -5,9 +5,13 @@ impressionist
 
 A lightweight plugin that logs impressions per action or manually per model
 
-I would not call this a stable plugin yet, although I have been running it in prod with no problems.  Use at your own risk ;-)
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+NOTE: If you are upgrading from a version prior to 0.4.0, you will need to run this migration after the upgrade:
+https://github.com/charlotte-ruby/impressionist/blob/master/upgrade_migrations/version_0_4_0.rb
+If you don't run this migration you will receive this error: Unknown attribute : referrer
+
+
 What does this thing do?
 ------------------------
 Logs an impression... and I use that term loosely.  It can log page impressions (technically action impressions), but it is not limited to that.