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+# Upgrade guide
+
+## v1.5.1 -> v1.5.2
+
+Version 1.5.2 adds are new column to the `impressions` table. If you're on v1.5.1 you need to manually add the new column using
+
+```
+add_column :impressions, :params, :text
+
+add_index :impressions, [:impressionable_type, :impressionable_id, :params], :name => "poly_params_request_index", :unique => false
+```
+
+before upgrading.