Moody's Investors Corp. ($68.62 0.67%) described the qualified mortgage rule as credit positive in a research note Monday.

Still, the ratings giant believes QM's 43% debt-to-income ratio ceiling will "suppress 9% of the prime jumbo mortgage market."

"Prime jumbo mortgage loans with common features such as DTIs higher than 43% and interest-only features are not qualified mortgages under the rule," Moody's explained.

Moody's has rated $2.3 billion of prime jumbo RMBS since March. Of that amount, 15% of the company's rated, prime jumbo RMBS does not fall within the guidelines of the qualified mortgage rule since the loans include interest-only features or DTIs that exceed the QM threshold.