A method for the production of a mechanically stabilized polyazole polymer membrane or film having the following steps: a) providing a membrane or film containing i.) a polyazole with at least one amino group in a repeating unit except the ones obtained by reacting aromatic and/or heteroaromatic diaminocarboxylic acids, ii.) at least one strong acid and iii.) at least one stabilizing reagent, the total content of stabilizing reagents in the membrane or film being within the range of from 0.01 to 30% by weight, b) performing the stabilization reaction in the membrane, immediately or in a subsequent processing step of the membrane, c) optionally doping the membrane obtained in accordance with step b) with a strong acid or concentrating the present strong acid by removal of present water, wherein the stabilizing reagent contains at least one oxazine-based compound and wherein the polyazole polymer has at least 1.8 dl/g intrinsic viscosity.