Solid forms of the compound, [5-(5-chloro-1H-pyrrolo[2,3-b]pyridin-3-ylmethyl)-pyridin-2-yl]-(6-trifluoromethyl-pyridin-3-ylmethyl)-amine HCl salt (Compound I) and its free base, active on the receptor protein kinases c-Kit and/or c-Fms and/or Flt3, were prepared and characterized: Also provided are methods of using the solid forms.