grafana/k6 · error

unable to use type %T as a duration value

Error message

unable to use type %T as a duration value

What it means

Raised by getInt64 (a helper behind GetDurationValue) when the duration option's value is of a Go type the helper does not handle — typically a JavaScript value that could not be narrowed to a numeric or string type. %P-style placeholder reports the actual type.

Source

Thrown at lib/types/types.go:189

	case int32:
		return int64(n), nil
	case int64:
		return n, nil
	case uint:
		return int64(n), nil //nolint:gosec
	case uint8:
		return int64(n), nil
	case uint16:
		return int64(n), nil
	case uint32:
		return int64(n), nil
	case uint64:
		if n > math.MaxInt64 {
			return 0, fmt.Errorf("%d is too big", n)
		}
		return int64(n), nil
	default:
		return 0, fmt.Errorf("unable to use type %T as a duration value", v)
	}
}

// GetDurationValue is a helper function that can convert a lot of different
// types to time.Duration.
//
// TODO: move to a separate package and check for integer overflows?
func GetDurationValue(v any) (time.Duration, error) {
	switch d := v.(type) {
	case time.Duration:
		return d, nil
	case string:
		return ParseExtendedDuration(d)
	case float32:
		return time.Duration(float64(d) * float64(time.Millisecond)), nil
	case float64:
		return time.Duration(d * float64(time.Millisecond)), nil
	default:

View on GitHub (pinned to 01ffac6f24)

Solutions

1. Pass durations as strings ("30s") or numbers
2. Avoid passing objects, arrays, booleans or null as duration values

When it happens

Trigger: Thrown at lib/types/types.go:189 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of grafana/k6@01ffac6f24 (2026-08-18). Data as JSON: /api/errors/b199eacfa9e112e3. Report an issue: GitHub.