diff --git a/lib/generators/active_record/templates/create_impressions_table.rb b/lib/generators/active_record/templates/create_impressions_table.rb
index 5282380..c874863 100644
--- a/lib/generators/active_record/templates/create_impressions_table.rb
+++ b/lib/generators/active_record/templates/create_impressions_table.rb
@@ -14,7 +14,7 @@ class CreateImpressionsTable < ActiveRecord::Migration
       t.text :referrer
       t.timestamps
     end
-    add_index :impressions, [:impressionable_type, :message, :impressionable_id], :name => "impressionable_type_message_index", :unique => false
+    add_index :impressions, [:impressionable_type, :message, :impressionable_id], :name => "impressionable_type_message_index", :unique => false, :length => {:message => 255 }
     add_index :impressions, [:impressionable_type, :impressionable_id, :request_hash], :name => "poly_request_index", :unique => false
     add_index :impressions, [:impressionable_type, :impressionable_id, :ip_address], :name => "poly_ip_index", :unique => false
     add_index :impressions, [:impressionable_type, :impressionable_id, :session_hash], :name => "poly_session_index", :unique => false