google/gson · error · IllegalArgumentException

JSON forbids NaN and infinities

Error message

JSON forbids NaN and infinities: ${value}

What it means

Standard JSON has no representation for NaN, +Infinity, or -Infinity. Unless the writer is in lenient mode, JsonTreeWriter.value(float) rejects Float.NaN, Float.POSITIVE_INFINITY, and Float.NEGATIVE_INFINITY with IllegalArgumentException. This prevents emitting JSON that other parsers would reject as malformed.

Solutions

1. Enable lenient mode: new GsonBuilder().setLenient().create(), or writer.setLenient(true)
2. Sanitize NaN/Infinity to null or a sentinel value before serialization
3. Register a custom TypeAdapter<Float> that converts NaN/Infinity to null

Example fix

// before - throws when f is NaN or Infinity
gson.toJson(myObj); // myObj has float f = Float.NaN

// after - enable lenient mode
Gson gson = new GsonBuilder().setLenient().create();
gson.toJson(myObj);

// Guard float before serializing unless lenient
float f = value;
if (!writer.isLenient() && (Float.isNaN(f) || Float.isInfinite(f))) {
    // replace with null, a sentinel, or enable lenient mode
    writer.nullValue();
} else {
    writer.value(f);
}

try {
  writer.value(f);
} catch (IllegalArgumentException e) {
  // 'JSON forbids NaN and infinities': set writer.setLenient(true) or sanitize f first
}

When it happens

Trigger: Serializing a float field whose runtime value is NaN or Infinity via a non-lenient Gson/JsonTreeWriter; computing a float from division by zero or undefined arithmetic and serializing it.

Common situations: Scientific/financial computations producing Infinity (division by zero) or NaN (0.0/0.0); sensor data with missing readings encoded as NaN; migrating from lenient to strict mode.

Related errors

• Did not expect a name
• Expected one JSON element but was
• Expecting number, got
• Incomplete document
• Please begin an object before writing a name.

AI-assisted analysis of google/gson@310ac341f2 (2026-08-10). Data as JSON: /api/errors/4ecb65b2a4551a1c. Report an issue: GitHub.

Appendix: source

Thrown at gson/src/main/java/com/google/gson/internal/bind/JsonTreeWriter.java:191

    put(new JsonPrimitive(value));
    return this;
  }

  @CanIgnoreReturnValue
  @Override
  public JsonWriter value(Boolean value) throws IOException {
    if (value == null) {
      return nullValue();
    }
    put(new JsonPrimitive(value));
    return this;
  }

  @CanIgnoreReturnValue
  @Override
  public JsonWriter value(float value) throws IOException {
    if (!isLenient() && (Float.isNaN(value) || Float.isInfinite(value))) {
      throw new IllegalArgumentException("JSON forbids NaN and infinities: " + value);
    }
    put(new JsonPrimitive(value));
    return this;
  }

  @CanIgnoreReturnValue
  @Override
  public JsonWriter value(double value) throws IOException {
    if (!isLenient() && (Double.isNaN(value) || Double.isInfinite(value))) {
      throw new IllegalArgumentException("JSON forbids NaN and infinities: " + value);
    }
    put(new JsonPrimitive(value));
    return this;
  }

  @CanIgnoreReturnValue
  @Override
  public JsonWriter value(long value) throws IOException {

View on GitHub (pinned to 310ac341f2)