unique index not working

gistfile1.txt

Sequel.migration do
  up do
    create_table :locations do
      primary_key :id
      String :address
      String :lat
      String :long
      DateTime :created_at
      DateTime :updated_at
    end

    add_index :locations, [:address, :lat, :long], :unique => true
  end

  down do
    drop_table :corporations
  end
end

migration log

INFO -  Begin applying migration version 3, direction: up
   INFO -  (0.007078s) BEGIN
   INFO -  (0.009243s) CREATE TABLE "locations" ("id" serial PRIMARY KEY, "address" text, "lat" text, "long" text, "created_at" timestamp, "updated_at" timestamp)
   INFO -  (0.009447s) CREATE UNIQUE INDEX "locations_address_lat_long_index" ON "locations" ("address", "lat", "long")
   INFO -  (0.001128s) UPDATE "schema_info" SET "version" = 3
   INFO -  (0.007561s) COMMIT
   INFO -  Finished applying migration version 3, direction: up, took 0.037248 seconds