google/gson · error · MalformedJsonException

JSON forbids NaN and infinities: ${d}; at path ${in.getPrevi

Error message

JSON forbids NaN and infinities: ${d}; at path ${in.getPreviousPath()}

What it means

Thrown by the LONG_OR_DOUBLE ToNumberStrategy when a JSON numeric token parses to Double.NaN or Double.POSITIVE/NEGATIVE_INFINITY and the JsonReader is NOT in lenient mode. Standard JSON forbids NaN and infinities, so Gson rejects them in strict/legacy mode. The message includes the offending value and the JSON path.

Source

Thrown at gson/src/main/java/com/google/gson/ToNumberPolicy.java:88

    @Override
    public Number readNumber(JsonReader in) throws IOException, JsonParseException {
      String value = in.nextString();
      if (value.indexOf('.') >= 0) {
        return parseAsDouble(value, in);
      } else {
        try {
          return Long.parseLong(value);
        } catch (NumberFormatException e) {
          return parseAsDouble(value, in);
        }
      }
    }

    private Number parseAsDouble(String value, JsonReader in) throws IOException {
      try {
        Double d = Double.valueOf(value);
        if ((d.isInfinite() || d.isNaN()) && !in.isLenient()) {
          throw new MalformedJsonException(
              "JSON forbids NaN and infinities: " + d + "; at path " + in.getPreviousPath());
        }
        return d;
      } catch (NumberFormatException e) {
        throw new JsonParseException(
            "Cannot parse " + value + "; at path " + in.getPreviousPath(), e);
      }
    }
  },

  /**
   * Using this policy will ensure that numbers will be read as numbers of arbitrary length using
   * {@link BigDecimal}.
   */
  BIG_DECIMAL {
    @Override
    public BigDecimal readNumber(JsonReader in) throws IOException {
      String value = in.nextString();

View on GitHub (pinned to 310ac341f2)

Solutions

1. Switch to ToNumberPolicy.LAZILY_PARSED_NUMBER or ToNumberPolicy.DOUBLE which handle special values without this guard
2. Set the JsonReader to Strictness.LENIENT if the source legitimately uses NaN/Infinity
3. Fix the data source to emit valid JSON numbers (null for NaN/Infinity, or string representations)

Example fix

// before
gsonBuilder.setObjectToNumberStrategy(ToNumberPolicy.LONG_OR_DOUBLE);

// after
gsonBuilder.setObjectToNumberStrategy(ToNumberPolicy.LAZILY_PARSED_NUMBER);

// Check for NaN/Infinity literals before deserializing with LONG_OR_DOUBLE
String raw = jsonNode.get("value").getAsString();
if ("NaN".equals(raw) || "Infinity".equals(raw) || "-Infinity".equals(raw)) {
  // decide: coerce to null, use Double, or reject
  return null;
}

try {
  return gson.fromJson(json, type);
} catch (MalformedJsonException e) {
  if (e.getMessage().contains("forbids NaN")) {
    // switch to a lenient reader or LAZILY_PARSED_NUMBER strategy
    return parseLenient(json, type);
  }
  throw e;
}

When it happens

Trigger: Deserializing numbers using ToNumberPolicy.LONG_OR_DOUBLE (set via GsonBuilder.setObjectToNumberStrategy or setNumberToNumberStrategy) where the JSON contains the literals NaN, Infinity, or -Infinity, and the reader strictness is not LENIENT.

Common situations: Non-JSON-compliant APIs or legacy systems that emit NaN/Infinity; switching the number strategy to LONG_OR_DOUBLE without checking source data; scientific/financial feeds using non-standard number tokens.

Related errors

• Cannot parse ${value}; at path ${in.getPreviousPath()}
• String contains non-ASCII characters: ${s} at path ${path}
• cannot deserialize ${baseType} because it does not define a
• cannot deserialize ${baseType} subtype named ${label}; did y
• Failed to parse date [${input}]: ${fail.getMessage()}

AI-assisted analysis of google/gson@310ac341f2 (2026-08-10). Data as JSON: /api/errors/5635c080b1116bc7. Report an issue: GitHub.