To prevent profit shifting by manipulation of transfer prices, tax authorities typically apply the arm's length principle in corporate taxation and use comparable market prices to ‘correctly' assess the value of intracompany trade and royalty income of multinationals. We develop a model of firms subject to financing frictions and offshoring of intermediate inputs. We find that arm's length prices systematically differ from prices set by independent agents. Application of the principle distorts multinational activity by reducing debt capacity and investment of foreign affiliates. Although it raises tax revenue and welfare in the headquarter country, welfare losses may be larger in the subsidiary location, leading to a loss in world welfare.