Y-chromosomal SNP markers are becoming increasingly more popular among forensic geneticists, but since they constitute variants specific to the ethnic origin, detailed population studies are required. Research into frequency of haplogroup N-M46 in the Belarusian population detected a mutated allele in 22 males, including one with a very distinct Y-STR haplotype. Sequencing of the M46 locus of this individual revealed the presence of a novel Y-SNP nearby the M46 locus, which was responsible for the erroneous assignment of the Y chromosome to the haplogroup N-M46. An impact of the identified polymorphism on discrimination of alleles of the M46 locus with various techniques was discussed, and solutions ensuring correctness of the genotyping results were proposed.