X0306 4 2017-01-20 0 0001160308 Mast Therapeutics, Inc. MSTX 0001363683 Greenleaf Peter 805 KING FARM BOULEVARD SUITE 550 ROCKVILLE MD 20850 1 0 0 0 Restricted Stock Units 2017-01-20 4 A 0 45535 0.00 A Common Stock 45535 45535 D Each restricted stock unit represents a contingent right to receive one share of the issuer's common stock. The restricted stock units vest in full upon consummation of the merger transaction contemplated by the Agreement and Plan of Merger, dated January 6, 2017, by and among the issuer, Savara Inc., and Victoria Merger Corp. (provided such event occurs on or before July 6, 2017). /s/ Brandi L. Roberts, Attorney-in-Fact for Peter Greenleaf 2017-01-23