
Attach (recommended) or Link to PDF file here:
[NAPEN16171380959.pdf](https://github.com/mozilla/pdf.js/files/6143802/NAPEN16171380959.pdf)

Configuration:
- Web browser and its version: Firefox 88 Nightly
- Operating system and its version: Windows 10
- PDF.js version:
- Is a browser extension: No

What went wrong? (add screenshot)
![](https://user-media-prod-cdn.itsre-sumo.mozilla.net/uploads/images/2021-03-15-10-58-27-ce2796.png)


source,
        sourceStart,
        sourceEnd,
        dest,
        destStart,
        hintsValid
      ) {
        var glyphProfile = {
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          sizeOfInstructions: 0,
        };
        if (sourceEnd - sourceStart <= 12) {
          
          return glyphProfile;
        }
        var glyf = source.subarray(sourceStart, sourceEnd);
        var contoursCount = signedInt16(glyf[0], glyf[1]);
        if (contoursCount < 0) {
          
          contoursCount = -1;
          writeSignedInt16(glyf, 0, contoursCount);
          
          dest.set(glyf, destStart);
          glyphProfile.length = glyf.length;
          return glyphProfile;
        }
        var i,