The ground-state rotational spectra of the five isotopomers C4H4O...(HBr)-Br-79, C4H4O...(HBr)-Br-81, C4D4O...(HBr)-Br-79, C4H4O...(DBr)-Br-79, and C4H4O...(DBr)-Br-81 of a weakly bound complex formed by furan with hydrogen bromide in the gas phase have been observed with a pulsed-jet, Fourier-transform instrument. Each spectrum was analyzed and fitted to give rotational constants A(0), B-0, and C-0, centrifugal distortion constants Delta(J) and Delta(JK), and components chi(aa), chi(bb)-chi(cc), and chi(ab) (or chi(ac) in the case of C4D4O...(HBr)-Br-79) of the bromine nuclear quadrupole coupling tensor. A detailed analysis of the spectroscopic constants reveals that the observed complex does not have C-2v symmetry, with HBr lying along the C-2 axis of furan. Instead, the geometry is of the face-on type, with the Br atom of HBr lying close to the perpendicular drawn through the center of the mass of the furan ring. The H atom of HBr lies between the Br atom and the face of the furan ring. The angles alpha(az) made by the HBr internuclear axis z with the a axis has the two possible values +/-11.929degrees. The preferred structure is that generated when the positive value of the angle is chosen and has the HBr subunit pointing in the direction of the O atom of furan. The determined geometrical parameters are r(O...H)=2.599(3) Angstrom, phi=112.90(14)degrees, and theta=6.05(4)degrees, where phi is the angle made by the O...H internuclear line with the local C-2 axis of furan and theta is the angular deviation of the O...H-Br nuclei from collinearity. Reasons why furan.HCl, but not furan...HBr, obeys some simple rules for predicting angular geometries are discussed.