# Using Strings for uint256 not working with ERC721EnumerableUpgradeable

**URL:** <https://forum.openzeppelin.com/t/using-strings-for-uint256-not-working-with-erc721enumerableupgradeable/20927>\
**Category:** Smart Contracts\
**Tags:** erc721, upgrades, upgrades-plugins\
**Created:** [December 13, 2021, 11:08pm UTC](https://forum.openzeppelin.com/t/using-strings-for-uint256-not-working-with-erc721enumerableupgradeable/20927 "2021-12-13T23:08:59Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![Thomas](https://sea2.discourse-cdn.com/flex022/user_avatar/forum.openzeppelin.com/thomas/32/11308_2.png) [@Thomas](https://forum.openzeppelin.com/u/Thomas)\
**Post date:** [December 13, 2021, 11:08pm UTC](https://forum.openzeppelin.com/t/using-strings-for-uint256-not-working-with-erc721enumerableupgradeable/20927/1 "2021-12-13T23:08:59Z")

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Hello, just like the title says I cannot get using Strings to compile, I keep getting the identifier not found.  
This is the start of my .sol contract

```auto
import "@openzeppelin/contracts-upgradeable/token/ERC721/extensions/ERC721EnumerableUpgradeable.sol";
import "@openzeppelin/contracts-upgradeable/access/OwnableUpgradeable.sol";
import "@openzeppelin/contracts-upgradeable/proxy/utils/Initializable.sol";
import "@openzeppelin/contracts-upgradeable/utils/StringsUpgradeable.sol";

contract NFT is Initializable, StringsUpgradeable, ERC721EnumerableUpgradeable, OwnableUpgradeable {
using Strings for uint256; 

```

Please help!

Thank you!

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<div class="post-metadata">

**Author:** ![asmel](https://sea2.discourse-cdn.com/flex022/user_avatar/forum.openzeppelin.com/asmel/32/11994_2.png) [@asmel](https://forum.openzeppelin.com/u/asmel)\
**Post date:** [December 14, 2021, 5:17am UTC](https://forum.openzeppelin.com/t/using-strings-for-uint256-not-working-with-erc721enumerableupgradeable/20927/2 "2021-12-14T05:17:13Z")

</div>

try changing String to StringsUpgradeable

using StringsUpgradeable for uint256;

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<div class="post-metadata">

**Author:** ![Thomas](https://sea2.discourse-cdn.com/flex022/user_avatar/forum.openzeppelin.com/thomas/32/11308_2.png) [@Thomas](https://forum.openzeppelin.com/u/Thomas)\
**Post date:** [December 14, 2021, 1:36pm UTC](https://forum.openzeppelin.com/t/using-strings-for-uint256-not-working-with-erc721enumerableupgradeable/20927/3 "2021-12-14T13:36:10Z")

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Thank you very much, it worked!!