Two of the most used sources for distributions of cacti (Cactaceae) indicate the family's northern range limit is either 58°N or 58°15′N for Opuntia fragilis. However these sources overstate the range limit by almost two degrees, an error that probably originated as a simple misreading of the latitude of Fort St. John. I discuss records of O. fragilis at and just south of 56°17′ N along the Peace River valley between Fort St. John, British Columbia and Peace River, Alberta, as well as why it is surprising but unlikely that specimens currently exist farther north. An error in latitude of 2° (223 km) in range can adversely affect ability to empirically estimate effects of climate change.