Government agencies including border control have an interest to detect if someone provides false information about their nationality. While response time tasks have been proposed to be able to detect someone’s true nationality, there is the risk that they will often err, particularly in the face of information contamination (i.e. someone having thorough knowledge of the country). We screened 2,200 participants to create three groups: Dutch participants (n = 118), and British participants with (n = 99) and without knowledge of the Netherlands (n = 118). They were tested with either the autobiographical Implicit Association Test (aIAT) or the Inducer-Concealed Information Test (I-CIT). While both tests could discriminate Dutch participants from British participants without knowledge of the Netherlands (AUCI-CIT = .65; AUCaIAT = .88), only the aIAT could also discriminate Dutch participants from British participants with knowledge (AUCI-CIT = .52; AUCaIAT = .86). Therefore, the aIAT, but not the I-CIT, could be a helpful tool to detect false nationality claims, even when information contamination is suspected.