diff --git a/src/OpenDirectoryDownloader/Helpers/FileSizeHelper.cs b/src/OpenDirectoryDownloader/Helpers/FileSizeHelper.cs
index c5c35dd8..12978d97 100644
--- a/src/OpenDirectoryDownloader/Helpers/FileSizeHelper.cs
+++ b/src/OpenDirectoryDownloader/Helpers/FileSizeHelper.cs
@@ -120,12 +120,17 @@ public static long ParseFileSize(string value, int kbValue = 1024, bool throwExc
         private static readonly string[] sizeSuffixes = { "B", "kiB", "MiB", "GiB", "TiB", "PiB", "EiB", "ZiB", "YiB" };
         private static readonly string[] sizeSuffixesBit = { "b", "kib", "Mib", "Gib", "Tib", "Pib", "Eib", "Zib", "Yib" };
 
-        public static string ToHumanReadable(long size, bool useBits = false)
+        public static string ToHumanReadable(long? size, bool useBits = false)
         {
             Debug.Assert(sizeSuffixes.Length > 0);
 
             const string formatTemplate = "{0}{1:#.##} {2}";
 
+            if (size == null)
+            {
+                return "-";
+            }
+
             if (size == 0)
             {
                 return string.Format(formatTemplate, null, 0, sizeSuffixes[0]);