features [@Strohmayer2019]. Hence, when [SAX J1808]{}began a new outburst in August 2019 [@ATelRussell19; @ATelGoodwin19; @ATelParikh19c; @ATelBult19c], we triggered an extensive [*NICER*]{}monitoring campaign. During this campaign we detected two X-ray bursts; the first occurred on August 9 and was relatively faint, the second was seen on August 21 and was much brighter. In this Letter we report on the unusual properties of the August 21 X-ray burst. The detailed analysis of the earlier burst and the full [*NICER*]{}campaign will be presented elsewhere.

Observations {#sec:observations}
============

On 2019 August 21 at 02:04 UTC, [*NICER*]{}observed a bright X-ray burst from [SAX J1808]{}. These data are available under the [*NICER*]{}ObsID 2584010501. We processed the data using <span style="font-variant:small-caps;">nicerdas</span> v6a, which is packaged with <span style="font-variant:small-caps;">heasoft</span> v6.26. We applied standard screening criteria, keeping only those time intervals when the pointing offset was $<54\arcsec$, the Earth limb elevation angle was $>15\arcdeg$, the elevation angle with respect to the bright Earth limb was $>30\arcdeg$, and the instrument was outside of the geographic region of the South Atlantic Anomaly. Additionally, standard background screening criteria were applied, which reject all epochs where the rate of saturating particle events (overshoots) is greater than $1$[ct[s$^{-1}$]{}]{}[detector$^{-1}$]{}, or greater than 1.52 \* <span 