diff --git a/VoidCat/Model/RangeRequest.cs b/VoidCat/Model/RangeRequest.cs
index bba1a38..8b40c52 100644
--- a/VoidCat/Model/RangeRequest.cs
+++ b/VoidCat/Model/RangeRequest.cs
@@ -7,7 +7,7 @@ public sealed record RangeRequest(long? TotalSize, long? Start, long? End)
     public string OriginalString { get; private init; }
     
     public long? Size
-        => (Start.HasValue ? (End ?? Math.Min(TotalSize!.Value, Start.Value + DefaultBufferSize)) - Start.Value : End) + 1L;
+        => (Start.HasValue ? (End ?? Math.Min(TotalSize!.Value - 1, Start.Value + DefaultBufferSize)) - Start.Value : End) + 1L;
 
     /// <summary>
     /// Return Content-Range header content for this range