This paper analyses the impact of banking mergers on systemic risk, with in particular if internationalization prior to acquisition increases systemic risk. By using the marginal expected shortfall methodology for an international sample of mergers, a significant increase in systemic risk is found as a result of mergers in the financial sector. Moreover, if a bank is operating internationally prior to acquisition, this increases systemic risk. Additionally, there is evidence of a too-big-to-fail motive for relatively smaller banks to use mergers to become systemically important. The results confirm that consolidation in the financial sector increases fragility of the financial system.