Provided herein are crystalline and salt forms of methyl N-{(1R)-2-[(2S)-2-{5-[4-(6-{2-[(2S)-1-{(2S)-2-[(methoxycarbonyl)amino]-3-methylbutanoyl} pyrrolidin-2-yl]-3H-benzimidazol-5-yl}thieno[3,2-b]thiophen-3-yl)phenyl]-1H-imidazol-2-yl}pyrrolidin-1-yl]-2-oxo-1-phenylethyl} carbamate, a Flaviviridae, including hepatitis C, virus inhibitor, pharmaceutical compositions comprising the compound, and processes of preparation thereof. Also provided are methods of its use for the treatment of a Flaviviridae, including HCV, infection in a subject in need thereof.