JamesNK/Newtonsoft.Json · error · InvalidOperationException

Can not convert from BigInteger to {0}.

Error message

Can not convert from BigInteger to {0}.

What it means

ConvertUtils.FromBigInteger (ConvertUtils.cs:337-368) converts a BigInteger into a target type. It handles decimal, double, float, ulong, and bool directly, then falls back to System.Convert.ChangeType((long)i, targetType). If that throws (target isn't convertible from long — e.g. string, Guid, DateTime — or the value overflows long), the exception is wrapped and rethrown as InvalidOperationException at ConvertUtils.cs:366.

Source

Thrown at Src/Newtonsoft.Json/Utilities/ConvertUtils.cs:366

            {
                return (float)i;
            }
            if (targetType == typeof(ulong))
            {
                return (ulong)i;
            }
            if (targetType == typeof(bool))
            {
                return i != 0;
            }

            try
            {
                return System.Convert.ChangeType((long)i, targetType, CultureInfo.InvariantCulture);
            }
            catch (Exception ex)
            {
                throw new InvalidOperationException("Can not convert from BigInteger to {0}.".FormatWith(CultureInfo.InvariantCulture, targetType), ex);
            }
        }
#endif

#region TryConvert
        internal enum ConvertResult
        {
            Success = 0,
            CannotConvertNull = 1,
            NotInstantiableType = 2,
            NoValidConversion = 3
        }

        [RequiresUnreferencedCode(MiscellaneousUtils.TrimWarning)]
        [RequiresDynamicCode(MiscellaneousUtils.AotWarning)]
        public static object Convert(object initialValue, CultureInfo culture, Type targetType)
        {
            switch (TryConvertInternal(initialValue, culture, targetType, out object? value))

View on GitHub (pinned to 4f73e74372)

Solutions

1. Map the BigInteger to one of the directly supported targets: decimal, double, float, ulong, bool, or a long-convertible type (int/long/short).
2. For string output, add a custom JsonConverter that returns bi.ToString(CultureInfo.InvariantCulture).
3. For Guid/DateTime targets, convert via an intermediate string and parse explicitly.
4. Guard against overflow: check bi against target min/max before conversion.

Example fix

// before: BigInteger -> string throws inside Convert.ChangeType
// after: custom converter
public override void WriteJson(JsonWriter w, object v, JsonSerializer s)
    => w.WriteValue(((BigInteger)v).ToString(CultureInfo.InvariantCulture));

// Route BigInteger to a supported target type; convert others explicitly.
static object SafeFromBigInteger(BigInteger i, Type target) {
    if (target == typeof(string)) return i.ToString(System.Globalization.CultureInfo.InvariantCulture);
    if (target == typeof(Guid)) return Guid.Empty; // or parse from string
    if (target == typeof(DateTime)) throw new InvalidOperationException("Map via string manually.");
    return ConvertUtils.FromBigInteger(i, target); // decimal/double/float/ulong/bool/long-convertible
}

static bool CanFromBigInteger(Type t) => t == typeof(decimal) || t == typeof(double) || t == typeof(float) || t == typeof(ulong) || t == typeof(bool) || t == typeof(long) || t == typeof(int) || t == typeof(short) || t == typeof(byte) || t == typeof(string);

try { return ConvertUtils.FromBigInteger(i, target); } catch (InvalidOperationException) { /* handle string/guid/datetime explicitly */ }

When it happens

Trigger: Deserializing a large integer into a target type that cannot be produced from a long: string, Guid, DateTime, TimeSpan, Uri, or a custom type with no long conversion; or a BigInteger whose magnitude exceeds long range being narrowed.

Common situations: BigInteger values mapped to string/DateTime/Guid properties; overflow when a very large BigInteger is narrowed into int/long; custom types without a long-based TypeConverter.

Related errors

• Cannot convert {0} to BigInteger.
• Can not convert {0} to BigInteger.
• Can not convert null {0} into non-nullable {1}.
• Target type {0} is not a value type or a non-abstract class.
• Can not convert from {0} to {1}.

AI-assisted analysis of JamesNK/Newtonsoft.Json@4f73e74372 (2026-08-07). Data as JSON: /api/errors/ba0c0f9bb1bb2f98. Report an issue: GitHub.