The business, which has lacked a permanent boss since January, has been forced to restate its total debt.
Kier Group’s total debt is now £180.5m, up from around £130m, which it had announced in its last trading update.
In addition to the £40m of misclassified debt, Kier said it had “identified a number of adjustments” that totalled £10.3m in relation to the group’s hedging activities. Kier Group is audited by Big Four firm PwC.
Stocks fell 13% after the news of the debt misclassification broke.
In December 2018, shares in the business almost halved as it announced a plan to sell new shares to existing investors at a one-third discount, in an aim to cut back its then net debt of more than £600m. That debt was underwritten by Kier Group’s bankers, and it shed the majority of its debt pile.
Interim results are set to be published 20 March.