A foldback triplex-forming oligonucleotide comprising a duplex forming region, a triplex forming region, and a linker region, wherein the duplex forming region is complementary to a region of a target nucleic acid and hybridizes to that region, thereby forming a duplex, and wherein the triplex forming region is complementary to the duplex forming region and hybridizes with the duplex formed between the duplex forming region and the target nucleic acid and thereby forms a triplex, and wherein the triplex forming region also comprises one or two abasic linkers that match up against a pyrimidine nucleotide of the target sequence, and wherein the linker region comprises a single covalent linkage or a flexible chemical moiety that connects the duplex forming region and the triplex forming region.