The invention relates to a fibrous preform (40) for a turbine ring sector, obtained by three-dimensional weaving and comprising a first part (42) forming a base, two L-shaped parts forming a tab (44, 46) and having two arms, said first arm (44a, 46a) extending each one of the two lateral ends of the first part (42), and a second part (48b) connecting the two tabs (44, 46), a first strip (A) and a second strip (B) woven together forming the first arm (44a, 46a), a first portion of the body of the second arm (44b, 46b) and the first part (42) having a separating area therebetween located in the first arm (44a, 46a) and the first part (42), and a third woven strip (C) forming the second part (48b) and a second portion of the body of the second arm (44b, 46b) of each tab (44, 46).