Isochronous pivot for a timepiece resonator, with a flexure bearing, comprising at least one pair including two flexible strips (31, 32) each joining a first point of attachment (41, 42) of a first element to a second point of attachment (51, 52) of a second element, said first attachment points (41, 42) defining, with said respective second attachment points (51, 52), two main strip directions (DL1, DL2), said first element and said second element each being stiffer than each of said flexible strips, and each able to form a movable inertial element inside a said resonator, and said two main strip directions (DL1, DL2) defining a theoretical pivot axis at their intersection when said two flexible strips (31, 32) are coplanar, or at the intersection of their projections onto a reference plane parallel to said two flexible strips (31, 32) when said two flexible strips (31, 32) extend on two levels parallel to said reference plane but are not coplanar,each said flexible strip (31, 32) having a free length (L1, L2) between its two attachment points (41, 51, 42, 52), and having an axial distance (D1, D2) between said theoretical pivot axis and whichever of its two attachment points (41, 51, 42, 52) is farthest therefrom, and wherein, for each said flexible strip (31, 32), the main attachment point ratio (D1/L1, D2/L2) between said axial distance and said free length is greater than one,wherein said two main strip directions (DL1, DL2) define with said theoretical pivot axis a first apex angle whose value in degrees satisfies the relation f1(X α)<α<f2(X α), with f1(X α) = 108 + 67/(10X α -6), and f2(X α) = 113 + 67/(10X α -6), with X α = D1/L1 = D2/L2, wherein said two main strip directions (DL1, DL2) define with said theoretical pivot axis a first apex angle comprised between 115° and 130° inclusive,and wherein said pivot includes, in addition to a first pair including said two flexible strips (31, 32), each joining a first attachment point (41, 42) of a first element to a second attachment point (51, 52) of a second element, at least a second pair including two other flexible strips (33, 34) each joining, on the one hand, a primary attachment point (43, 44) of said first element or a secondary attachment point (53, 54) of said second element, to, on the other hand, a third attachment point (63, 64) comprised in a third element arranged to be fixedly secured to a fixed structure of said resonator, wherein said primary attachment points (43, 44) of said first element or secondary attachment points (53, 54) of said second element, on the one hand, and said tertiary attachment points (63, 64) on the other hand, define two secondary strip directions (DL3, DL4) together forming a second apex angle (β) at a secondary axis defined by the intersection, in plane or in projection, of said secondary strip directions (DL3, DL4), said second apex angle (β) being comprised between 115° and 130° inclusive, and whose value in degrees satisfies the relation f1(X β)<β<f2(X β), with f1(X β) = 108 + 67/(10 X β -6), and f2(X β) = 113 + 67/(10 X β -6), with X β = D3/L3 = D4/L4, characterised in that a median function fm = 110.5 + 67/(10X-6) defines an intermediate ratio between said first lower function f1 = 108 + 67/(10X-6), and said first upper function f2 = 113 + 67/(10X-6), with X = D/L, and in that said first apex angle and said second apex angle (β) are positioned between said first lower function f1 and said first upper function f2, on either side of said median function fm.