A provision adopted by several Southern states after Reconstruction that exempted citizens from new literacy tests and poll taxes if their ancestors had been eligible to vote prior to 1867, effectively preserving white electoral dominance while circumventing the Fifteenth Amendment. Declared unconstitutional in cases such as Guinn v. United States (1915), it played a central role in the systematic disenfranchisement of Black voters and prompted later federal voting-rights interventions.