Plaintiff, on behalf of debtor, filed a complaint against defendant seeking recovery of prepetition freight charges for debtor's transportation of goods for defendant. Based on stipulated facts, including that defendant had a valid prepetition claim against debtor that exceeded the valid freight charges, the bankruptcy court concluded that defendant's offset was precluded by the Interstate Commerce Act, which limits defenses that may be asserted in response to a claim for freight charges. Debtor argued that, since defendant had not raised any of the defenses under that Act, it could not claim an offset in the adversary proceeding and was limited to filing a proof of claim in the bankruptcy. The bankruptcy court agreed, and defendant appealed. The district court reversed, holding that 11 U.S.C. § 553 preserved defendant's offset claim in the bankruptcy. Since 11 U.S.C. § 542(b) precludes a turnover of debt that is subject to offset, defendant was entitled to assert its offset claim in defense of plaintiff's turnover claim.