function _updatePurchasingState(
    address _beneficiary,
    uint256 _weiAmount
  )
  internal
  {
    super._updatePurchasingState(_beneficiary, _weiAmount);
    contributions.addBalance(
      _beneficiary,
      _weiAmount,
      _getTokenAmount(_weiAmount)
    );

    transactionCount = transactionCount + 1;
  }