```\n/// @notice Adds an external ERC20 token type as an additional prize that can be awarded\n/// @dev Only the Prize-Strategy owner/creator can assign external tokens,\n/// and they must be approved by the Prize-Pool\n/// @param \_externalErc20 The address of an ERC20 token to be awarded\nfunction addExternalErc20Award(address \_externalErc20) external onlyOwnerOrListener {\n  \_addExternalErc20Award(\_externalErc20);\n}\n\nfunction \_addExternalErc20Award(address \_externalErc20) internal {\n  require(prizePool.canAwardExternal(\_externalErc20), "PeriodicPrizeStrategy/cannot-award-external");\n  externalErc20s.addAddress(\_externalErc20);\n  emit ExternalErc20AwardAdded(\_externalErc20);\n}\n```\n