We present the discovery of a new extreme high proper motion object (˜3.5 arcsec/year) which we classify as an ultracool subdwarf with [M/H] ˜ -0.5. It has a formal spectral type of sdM9 but also shows L-type features: while the VO bands are completely absent, it exhibits extremely strong TiO absorption in its optical spectrum. With a radial velocity of about -160 km s-1 and a rough distance estimate of 16-24 pc, it is likely one of the nearest halo members crossing the Solar neighbourhood with a heliocentric space velocity of (U,V,W)=(-244,-256,-100)±(32,77,6) km s-1. Based on archival data from the SuperCOSMOS Sky Surveys, 2MASS, and DENIS, and observations with the ESO 3.6-m telescope (ESO 072.C-0630) and VLT (ESO 072.C-0725).