Disclosed are crystalline free base ansolvate forms of 2-hydroxy-6-((2(lisopropyl-1H-pyrazol-5-yl)pyridin-3- yl)methoxy)benzaldehyde (or Compound 1), such as the free base Form I, Form II and Material N.Also disclosed are crystalline free base solvates of 2-hydroxy-6-((2-(l-isopropyl- lHpyrazol-5-yl)pyridin-3-yl)mefhoxy)benzaldehyde (or Compound 1).