The structural behavior of the Zr52Ti5Cu18Ni15Al10 bulk glass-forming alloy has been investigated in situ by means of high-temperature x-ray synchrotron diffraction. The dependence of the structure factor of the glass can be well described with a Debye–Waller factor and a Debye temperature θ=412 K. At the glass transition, the structure factor significantly decreases due to additional thermal excitations. The extrapolation of the structure factor of the supercooled liquid to temperatures above the liquidus curve is in agreement with experimentally determined values of the melt. The short-range order of the glass, of the supercooled liquid state, and of the equilibrium melt at T=1193 K, is found to be quite similar. The formation of complex chemically ordered clusters in the melt is proposed to be essential for the high-glass-forming ability of this alloy. © 2002 American Institute of Physics.