We develop a model for the prospective hedge effectiveness of cash flow hedges and find that the “highly effective” criterion of the FASB and IASB fails to recognize the scope of variation of the hedge effectiveness of pure hedges for different types of risk exposures. Prospective hedge effectiveness is not a reliable signal of a speculative component in a derivative portfolio and, consequently, the current “highly effective” screening mechanism cannot effectively separate pure hedges from derivative portfolios that are partly or fully influenced by speculation. We link these and other findings to the current efforts of the FASB and IASB to reform accounting for financial instruments.