AvaloniaUI/Avalonia · error · ArgumentException

Font stretch must be > 1.

Error message

Font stretch must be > 1.

What it means

Thrown by the Typeface constructor when FontStretch, cast to int, is less than 1. FontStretch values are positive integers (e.g. FontStretch.Normal is 5). A stretch of 0 or negative is invalid because the font selection pipeline cannot match it.

Source

Thrown at src/Avalonia.Base/Media/Typeface.cs:33

        /// Initializes a new instance of the <see cref="Typeface"/> class.
        /// </summary>
        /// <param name="fontFamily">The font family.</param>
        /// <param name="style">The font style.</param>
        /// <param name="weight">The font weight.</param>
        /// <param name="stretch">The font stretch.</param>
        public Typeface(FontFamily fontFamily,
            FontStyle style = FontStyle.Normal,
            FontWeight weight = FontWeight.Normal,
            FontStretch stretch = FontStretch.Normal)
        {
            if (weight <= 0)
            {
                throw new ArgumentException("Font weight must be > 0.");
            }
            
            if ((int)stretch < 1)
            {
                throw new ArgumentException("Font stretch must be > 1.");
            }

            FontFamily = fontFamily ?? FontFamily.Default;
            Style = style;
            Weight = weight;
            Stretch = stretch;
        }

        /// <summary>
        /// Initializes a new instance of the <see cref="Typeface"/> class.
        /// </summary>
        /// <param name="fontFamilyName">The name of the font family.</param>
        /// <param name="style">The font style.</param>
        /// <param name="weight">The font weight.</param>
        /// <param name="stretch">The font stretch.</param>
        public Typeface(string fontFamilyName,
            FontStyle style = FontStyle.Normal,
            FontWeight weight = FontWeight.Normal,

View on GitHub (pinned to 11c5427268)

Solutions

1. Use a valid FontStretch such as FontStretch.Normal (5) or FontStretch.Condensed (3).
2. Validate: if ((int)stretch < 1) stretch = FontStretch.Normal.
3. Ensure any deserialized stretch value falls in the valid positive range.

Example fix

// before
var typeface = new Typeface(family, stretch: (FontStretch)0); // throws

// after
var typeface = new Typeface(family, stretch: FontStretch.Normal);

static Typeface SafeTypefaceStretch(FontFamily f, FontStyle st, FontWeight w, FontStretch sr)
{
    if ((int)sr < 1) sr = FontStretch.Normal;
    return new Typeface(f, st, w, sr);
}

static bool IsValidStretch(FontStretch s) => (int)s >= 1;

When it happens

Trigger: Constructing a Typeface with stretch cast to int < 1, e.g. new Typeface(family, stretch: (FontStretch)0). This happens when an uninitialized or out-of-range stretch value is supplied.

Common situations: Casting a numeric config value to FontStretch where it is 0 or negative; default(FontStretch) confusion (the Normal default is 5, not 0); deserialization of a stretch field left unset.

Related errors

• Font weight must be > 0.
• Could not create glyphTypeface. Font family: {FontFamily?.Na
• No cmap table found.
• Invalid {nameof(TextRunProperties.FontRenderingEmSize)}
• {nameof(textLength)} ('0') must be a non-zero value.

AI-assisted analysis of AvaloniaUI/Avalonia@11c5427268 (2026-08-13). Data as JSON: /api/errors/658bbb32f7cd3b98. Report an issue: GitHub.