174031 2017-06-30 11:12:29 -0700 Safari always assumes mono-spaced square characters when loading fonts 2017-07-05 18:09:22 -0700 1 1 1 Unclassified WebKit CSS Safari 10 All All RESOLVED FIXED InRadar P2 Normal --- 1 dvoytenko webkit-unassigned mmaxfield webkit-bug-importer oldest_to_newest 1324471 0 dvoytenko 2017-06-30 11:12:29 -0700 See example: http://output.jsbin.com/jexixam/quiet Initially, before the "Slow" font-face has been loaded or timed out, the sample text takes about 2.5-3x more space to layout (on iOS, it takes about 8-9 lines and once the font is loaded/timed out, it takes only 3 lines). In other words, the estimate is too rough. It appears that Safari assumes mono-wide square characters, which is very uncommon. It might be a better option to use a fallback font to estimate character layout before the desired font is loaded (as in `font-family: Slow, Arial` where "Arial" is already available as the fallback). This would also reduce the work the browser has to do in case of timeout. 1324500 1 webkit-bug-importer 2017-06-30 13:17:35 -0700 <rdar://problem/33083545> 1325787 2 mmaxfield 2017-07-05 14:57:00 -0700 I think I fixed this in r216944. Can you see if the problem still reproduces on a nightly build? 1325854 3 dvoytenko 2017-07-05 18:09:22 -0700 Does appear to be fixed in nightly. Thanks for the fix!