google/gson · error · IllegalArgumentException

${value} is not a valid double value as per JSON specificati

Error message

${value} is not a valid double value as per JSON specification. To override this behavior, use GsonBuilder.serializeSpecialFloatingPointValues() method.

What it means

By default Gson uses a strict double/float adapter (DOUBLE_STRICT / FLOAT_STRICT) that rejects NaN and Infinity because they are not valid JSON values per the specification. The check fires during serialization when writing a double or float field. The error message tells you to call GsonBuilder.serializeSpecialFloatingPointValues() to switch to the lenient adapter.

Source

Thrown at gson/src/main/java/com/google/gson/internal/bind/TypeAdapters.java:521

    }

    @Override
    public void write(JsonWriter out, Number value) throws IOException {
      if (value == null) {
        out.nullValue();
        return;
      }
      double doubleValue = value.doubleValue();
      if (strict) {
        checkValidFloatingPoint(doubleValue);
      }
      out.value(doubleValue);
    }
  }

  private static void checkValidFloatingPoint(double value) {
    if (Double.isNaN(value) || Double.isInfinite(value)) {
      throw new IllegalArgumentException(
          value
              + " is not a valid double value as per JSON specification. To override this"
              + " behavior, use GsonBuilder.serializeSpecialFloatingPointValues() method.");
    }
  }

  public static final TypeAdapter<Number> FLOAT = new FloatAdapter(false);
  public static final TypeAdapter<Number> FLOAT_STRICT = new FloatAdapter(true);

  public static final TypeAdapter<Number> DOUBLE = new DoubleAdapter(false);
  public static final TypeAdapter<Number> DOUBLE_STRICT = new DoubleAdapter(true);

  public static final TypeAdapter<Character> CHARACTER =
      new TypeAdapter<Character>() {
        @Override
        public Character read(JsonReader in) throws IOException {
          if (in.peek() == JsonToken.NULL) {
            in.nextNull();

View on GitHub (pinned to 310ac341f2)

Solutions

1. Call new GsonBuilder().serializeSpecialFloatingPointValues().create() to allow NaN and Infinity in output
2. Sanitize the data before serialization by replacing NaN/Infinity with null or a sentinel value
3. Register a custom JsonSerializer for Double/Float that handles special values explicitly

Example fix

// before
Gson gson = new Gson();
gson.toJson(new Result(Double.NaN)); // throws IllegalArgumentException

// after
Gson gson = new GsonBuilder()
    .serializeSpecialFloatingPointValues()
    .create();
gson.toJson(new Result(Double.NaN)); // outputs "NaN"

// Check for NaN or Infinity before serializing
public static void replaceSpecialDoubles(Object obj) {
    for (Field f : obj.getClass().getDeclaredFields()) {
        if (f.getType() == double.class || f.getType() == Double.class) {
            f.setAccessible(true);
            Double v = (Double) f.get(obj);
            if (v != null && (Double.isNaN(v) || Double.isInfinite(v))) {
                f.set(obj, null); // or a sentinel value
            }
        }
    }
}

try {
    String json = gson.toJson(obj);
} catch (IllegalArgumentException e) {
    if (e.getMessage().contains("not a valid double value")) {
        // rebuild Gson with serializeSpecialFloatingPointValues() or sanitize data
        Gson lenient = new GsonBuilder().serializeSpecialFloatingPointValues().create();
        json = lenient.toJson(obj);
    }
}

When it happens

Trigger: Serializing an object with a double or float field whose value is Double.NaN, Double.POSITIVE_INFINITY, or Double.NEGATIVE_INFINITY using a default Gson instance.

Common situations: Computational results that produce NaN or Infinity (division by zero, indeterminate forms); sensor or measurement data with sentinel infinite values; porting from Jackson which allows these by default.

Related errors

• JSON forbids NaN and infinities: ${result}
• cannot serialize ${srcType.getName()}; did you forget to reg
• cannot serialize ${srcType.getName()} because it already def
• Cannot parse ${value}; at path ${in.getPreviousPath()}
• Deserialization is unsupported

AI-assisted analysis of google/gson@310ac341f2 (2026-08-10). Data as JSON: /api/errors/00cfe9dcee2fa5ee. Report an issue: GitHub.