google/gson · error · MalformedJsonException

JSON forbids NaN and infinities: {result}

Error message

JSON forbids NaN and infinities: {result}

What it means

JsonTreeReader.nextDouble throws MalformedJsonException('JSON forbids NaN and infinities: ' + result) when the parsed double value is NaN or +/-Infinity AND the reader is not lenient. Strict JSON (RFC 8259) does not permit NaN or Infinity literals; only lenient mode tolerates them. The {result} is the offending numeric value.

Source

Thrown at gson/src/main/java/com/google/gson/internal/bind/JsonTreeReader.java:254

    }
  }

  @Override
  public double nextDouble() throws IOException {
    JsonToken token = peek();
    if (token != JsonToken.NUMBER && token != JsonToken.STRING) {
      throw new IllegalStateException(
          "Expected " + JsonToken.NUMBER + " but was " + token + locationString());
    }
    JsonPrimitive primitive = (JsonPrimitive) peekStack();
    double result;
    try {
      result = primitive.getAsDouble();
    } catch (NumberFormatException e) {
      throw numberFormatException("Expected a double but was " + primitive.getAsString(), e);
    }
    if (!isLenient() && (Double.isNaN(result) || Double.isInfinite(result))) {
      throw new MalformedJsonException("JSON forbids NaN and infinities: " + result);
    }
    popStack();
    if (stackSize > 0) {
      pathIndices[stackSize - 1]++;
    }
    return result;
  }

  @Override
  public long nextLong() throws IOException {
    JsonToken token = peek();
    if (token != JsonToken.NUMBER && token != JsonToken.STRING) {
      throw new IllegalStateException(
          "Expected " + JsonToken.NUMBER + " but was " + token + locationString());
    }
    JsonPrimitive primitive = (JsonPrimitive) peekStack();
    if (token == JsonToken.STRING) {
      validateAscii(primitive.getAsString());

View on GitHub (pinned to 8b8628c656)

Solutions

1. Enable lenient mode: construct the JsonReader and call setLenient(true) before reading (note: Gson.fromJson defaults are strict).
2. Sanitize the source: replace NaN/Infinity with null or a sentinel value before building the tree.
3. Register a custom TypeAdapter for double/Double that converts NaN/Infinity to null or a defined sentinel on write and accepts it on read.
4. Validate upstream that the producer never emits NaN/Infinity.

Example fix

// before
JsonObject o = new JsonObject(); o.addProperty("v", Double.NaN);
JsonTreeReader r = new JsonTreeReader(o);
r.beginObject(); r.nextName();
r.nextDouble(); // MalformedJsonException: JSON forbids NaN and infinities: NaN

// after
JsonTreeReader r = new JsonTreeReader(o);
r.setLenient(true);
r.beginObject(); r.nextName();
r.nextDouble(); // returns NaN

// Sanitize NaN/Infinity in source doubles before building the tree
double sanitize(double v) {
  return Double.isNaN(v) || Double.isInfinite(v) ? 0.0d : v; // or use null wrapper
}

static boolean isJsonLegalDouble(double v) {
  return !Double.isNaN(v) && !Double.isInfinite(v);
}

JsonReader r = new JsonTreeReader(element);
r.setLenient(true); // opt-in to NaN/Infinity if the source may contain them
try {
  return r.nextDouble();
} catch (MalformedJsonException e) {
  if (e.getMessage() != null && e.getMessage().startsWith("JSON forbids NaN and infinities")) {
    throw new InvalidPayloadException("Numeric value not representable in strict JSON", e);
  }
  throw e;
}

When it happens

Trigger: Reading a JsonPrimitive holding Double.NaN, POSITIVE_INFINITY, or NEGATIVE_INFINITY through a non-lenient JsonTreeReader.nextDouble(). Common when the source tree was built from a Java object that had NaN/Infinity doubles and then re-serialized strictly.

Common situations: Math/finance code producing NaN or Infinity; sensor data with NaN sentinels; deserializing a tree that a lenient writer produced back through a strict reader; default Gson is non-lenient.

Related errors

• Expected NUMBER but was {token}{location}
• JsonReader is closed
• Expected {expected} but was {peek}{location}
• Expected STRING but was {token}{location}
• Primitive is neither a number nor a string

AI-assisted analysis of google/gson@8b8628c656 (2026-08-04). Data as JSON: /data/errors/d91c9cf9d8a20222.json. Report an issue: GitHub.