Composer require phpoffice/phpexcel not installing

Basically I'm trying to execute;

composer require phpoffice/phpexcel

And I get;

Using version ^1.8 for phpoffice/phpexcel
./composer.json has been updated

  Type error: Return value of Magento\InventoryComposerInstaller\Plugin_composer_tmp1::  
  initModuleDeployment() must be an instance of Magento\InventoryComposerInstaller\void  
  , none returned

Note: I am doing this within a Magento installation if that makes any difference.