The present invention relates to novel solid forms of compound (I) [(1S)-1-[(2S,4R,5R)-5-(5-amino-2-oxo-thiazolo[4,5-d]pyrimidin-3-yl)-4-hydroxy-tetrahydrofuran-2-yl]propyl] acetate and pharmaceutical compositions comprising the solid forms thereof disclosed herein, which may be used as a TLR7 agonist, or for the treatment or prophylaxis of a viral disease in a patient relating to HBV infection or a disease caused by HBV infection.