The present application relates to solid state forms, for example, crystalline forms of 2′-C-methyluridine-5′-(O-phenyl-N-(S)-1-(isopropoxycarbonyl)ethyl)thiophosphoramidate, pharmaceutical compositions that can include one or more solid forms of 2′-C-methyluridine-5′-(O-phenyl-N-(S)-1-(isopropoxycarbonyl)ethyl)thiophosphoramidate, and methods of treating or ameliorating diseases and/or conditions with one or more solid forms of 2′-C-methyluridine-5′-(O-phenyl-N-(S)-1-(isopropoxycarbonyl)ethyl)thiophosphoramidate. Also disclosed herein are methods of treating diseases and/or conditions with one or more solid forms of 2′-C-methyluridine-5′-(O-phenyl-N-(S)-1-(isopropoxycarbonyl)ethyl)thiophosphoramidate in combination with one or more other agents.