diff --git a/src/Npgsql.Json.NET/Internal/JsonNetJsonConverter.cs b/src/Npgsql.Json.NET/Internal/JsonNetJsonConverter.cs
index 5d75568f98..10126d25f9 100644
--- a/src/Npgsql.Json.NET/Internal/JsonNetJsonConverter.cs
+++ b/src/Npgsql.Json.NET/Internal/JsonNetJsonConverter.cs
@@ -51,7 +51,7 @@ static class JsonNetJsonConverter
         using var stream = reader.GetStream();
         var mem = new MemoryStream();
         if (async)
-            await stream.CopyToAsync(mem, Math.Min((int)mem.Length, 81920), cancellationToken).ConfigureAwait(false);
+            await stream.CopyToAsync(mem, Math.Min((int)stream.Length, 81920), cancellationToken).ConfigureAwait(false);
         else
             stream.CopyTo(mem);
         mem.Position = 0;