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 αs in three flavour tagged samples (uds, c and b). The event shape distributions were fitted by O(α2s) calculations of jet production taking into account mass effects for the c and b quarks. We find:
αcs/αuds = 0.997 ± 0.038 (stat.) ± 0.030 (syst.) ± 0.012 (theory) and
αbs/αuds = 0.993 ± 0.008 (stat.) ± 0.006 (syst.) ± 0.011 (theory).