  We present a test of the flavour independence of the strong coupling constant
for charm and bottom quarks with respect to light (uds) quarks, based on a
hadronic event sample obtained with the OPAL detector at LEP. Five observables
related to global event shapes were used to measure alpha_s in three flavour
tagged samples (uds, c and b). The event shape distributions were fitted by
Order(alpha_s**2) calculations of jet production taking into account mass
effects for the c and b quarks. We find: = 0.997 +- 0.038(stat.) +-
0.030(syst.) +- 0.012(theory) and = 0.993 +- 0.008(stat.) +- 0.006(syst.) +-
0.011(theory) for the ratios alpha_s(charm)/alpha_s(uds) and
alpha_s(b)/alpha_s(uds) respectively.
