In order to contribute to the literature on bank size as a determinant of systemic risk, this article assesses whether the banks’ size effects on banks’ systemic risk exposure in the European Banking Union could be mitigated/aggravated when the banking sector concentration is taken into account. The results indicate that the banking sector concentration lowers the banks’ size effects on banks’ systemic risk exposure in the European Banking Union. Thus, this article advocates for mergers and acquisitions between banks in the European Banking Union.