A method of sample analysis is provided. In certain embodiments, the method involves: a) amplifying a product from a sample that comprises both wild type copies of a genomic locus and mutant copies of the genomic locus that have a point mutation relative to said wild type copies of the genomic locus, to produce an amplified sample, where: i. the amplifying is done using a first primer and a second primer; and ii. the first primer comprises a 3′ terminal nucleotide that base pairs with the point mutation and also comprises a nucleotide sequence that is fully complementary to a sequence in the locus with the exception of a single base mismatch within 6 bases of the 3′ terminal nucleotide; and b) detecting the presence of said product in said amplified sample using a flap assay that employs an invasive oligonucleotide. A kit for performing the method is also provided.