The present invention relates to a binding molecule, in particular an antibody or binding fragment thereof, capable of activating FXII, which binds to the proline rich domain of FXII. In particular, the invention is directed to FXII activating antibodies or binding fragments thereof which binds to the proline rich domain of FXII. The invention also encompasses the use of the binding molecule directed to the proline rich domain of FXII as blood coagulation activator, e.g. in diagnostic blood coagulation tests. Corresponding methods and blood coagulation test are also encompassed.