The Bank of Japan racked up the most unrealized losses on its bond holdings on record in the latest six-month period, illustrating the challenge facing Gov. Kazuo Ueda if he moves toward normalizing policy.

The paper loss on those assets was ¥10.5 trillion ($70.7 billion) at the end of September, the largest loss in data going back to fiscal 2004, according to the central bank’s semiannual financial statement Tuesday. It’s more than six times bigger than the ¥157 billion loss tallied for last fiscal year.

The loss itself isn’t likely to deter Ueda from paring back stimulus if the bank’s inflation goal is achieved. Still, it’s an indication of the challenge ahead when the central bank eventually moves toward an exit, as most economists expect to see by the middle of next year. Even a minuscule rise in yields degrades the value of the bank’s massive bond holdings, which account for more than half of all the central government’s outstanding debt.