Cognitive biases and distortions are a common feature of the human condition. In gender research, two biases are well established: alpha bias which is the tendency to highlight sex differences and beta bias which is the tendency to minimise or play down sex differences (Hare-Mustin & Marecek, 1988). Last year we introduced the theory of gamma bias, which is the simultaneous shrinking and magnifying of gender differences (alpha and beta bias combined) resulting in the distortion of public perceptions of masculinity towards the negative and femininity towards the positive (Martin Seager & Barry, 2019). We now build on this theory by introducing a further concept: delta bias. Delta bias may be defined as the simultaneous denigration or celebration – depending on the gender of the performer – of an archetypal masculine gender behaviour or characteristic. This is similar to the ‘celebration’ aspect of gamma bias, except that delta bias emphasises how celebration tends to occur where the behaviour is gender atypical.