Learning the concept of fractions is among the most challenging topics in school mathematics. One of the main sources of difficulties in learning fractions is related to "natural number bias" (Van Hoof, Verschaffel & Van Dooren, 2015). Applying properties of the natural numbers incorrectly in situations involving rational numbers can lead individuals to make systematic errors. But natural number bias does not occur only when students first encounter fractions. It occurs again in different forms when students encounter fractions in different contexts. Here I argue that it is not enough to address natural number bias when fractions are first taught, it must be addressed each time fractions are used in a new way.