diff --git a/db/migrate/20110727073510_change_crypted_password_length.rb b/db/migrate/20110727073510_change_crypted_password_length.rb
index cdc1649c..9bd2c639 100644
--- a/db/migrate/20110727073510_change_crypted_password_length.rb
+++ b/db/migrate/20110727073510_change_crypted_password_length.rb
@@ -4,6 +4,17 @@ class ChangeCryptedPasswordLength < ActiveRecord::Migration
   end
 
   def self.down
+    # Begin with setting all passwords hashed with BCrypt to SHA-1 ones as
+    # BCrypt's format won't fit into a narrower column.
+    User.transaction do
+      User.all.each do |user|
+        if user.auth_type == 'database' and not user.uses_deprecated_password?
+          user.password = user.password_confirmation = nil
+          user.crypted_password = User.sha1 'change_me'
+          user.save!
+        end
+      end
+    end
     change_column 'users', 'crypted_password', :string, :limit => 40
   end
 end