BOGGS, Circuit Judge. Art Iron, Inc. contests whether the district court properly awarded summary judgment to Board of Trustees (“Board”) of the Shopmen’s Local 499 Pension Plan (“the Plan”). This suit arises from the Board’s pursuit of over one million dollars of withdrawal liability pursuant to the Employee Retirement Income Security Act of 1974 (“ERISA”) from Art Iron, Robert Schlatter, and Mary Schlatter.

Because Art Iron’s liability was not disputed, the only issue before the district court was whether Robert Schlatter, Art Iron’s sole shareholder at the time of withdrawal, and Mary Schlatter, his wife, were jointly and severally liable for Art Iron’s withdrawal liability. The Plan alleged that the Schlatters were each personally liable for Art Iron’s withdrawal liability because each ran a trade or business under “common control” with Art Iron.

Mr. Schlatter operated a consulting business as a sole proprietor and under common control with Art Iron. Pursuant to 29 U.S.C. § 1301(b)(1), the district court determined that Robert Schlatter was individually liable for the withdrawal liability. In its reasoning, the district court found that the consulting business was operated under common control with Art Iron and constituted a “trade or business” under 29 U.S.C. § 1301(b)(1).

Additionally, the district court found that Mrs. Schlatter also ran a sole proprietorship at the time of Art Iron’s withdrawal from the Plan and was individually liable for the withdrawal liability. Because Robert and Mary Schlatter had a minor son at the time, the district court found that both of their interests in the businesses they ran were also attributable to their son under Treasury Regulation 26 C.F.R. § 1.414(c)-4(b)(6). Therefore, the district court found that there was a group of trades or businesses under common control with Art Iron and granted summary judgment to the Board.

We affirm the district court’s judgment as to Robert Schlatter and reverse and remand the district court’s grant of summary judgment as to Mary Schlatter.