Horizon Pharma (HZNP - Get Report)  continued its M&A maneuvering on Monday with an $800 million agreement to buy Raptor Pharmaceutical  (RPTP) to expand its rare disease business and extend its international presence.

The Dublin company said it would offer $9a share for Novato, Calif.-based Raptor. That's almost 21% above Raptor's most recent price of $7.45 before trading in the shares was suspended.

Horizon bought Crealta for $510 million in January, just weeks after pulling a $3.4 billion hostile bid for Depomed (DEPO) . It said the addition of Raptor would boost its Ebitda in 2017 and bolster its business outside the U.S., in Europe and elsewhere. It will give it drugs including Procysbi to treat a rare metabolic disorder called nephropathic cystinosis and Quinsair for cystic fibrosis-related lung infections. Horizon also gets the chance to bolster its rare-disease revenue above the current 45% of total sales.

"Along with the potential for accelerated revenue growth, the addition of Raptor strengthens our U.S. orphan business and provides a platform to expand our orphan business in Europe and other key international markets," said Horizon Chairman Timothy P. Walbert in a statement.

Raptor President and CEO Julie Anne Smith said the deal will "deliver significant and immediate value to our shareholders."

Horizon said it will use $675 million of external debt along with cash on hand to pay for Raptor.

The companies expected the deal to close in the fourth quarter.

Horizon shares were inactive in premarket trading while Raptor shares jumped 20.5%.