In their recent manuscript Xie and colleagues argue that pigeon ISCA1 and CRY4 act as a magnetic protein biocompass asserting that they have unambiguously proved that these two proteins interact and form a complex with unique biophysical features. We do not think the evidence presented in their manuscript supports this conclusion. Firstly, we show that for all of their experiments Xie and colleagues employed the incorrect sequence of CRY4, which did not include the functionally critical C-terminal tail. Secondly, we demonstrate that both CRY4 and ISCA1 are broadly expressed in all pigeon tissues, lacking the spatially restricted expression pattern that would one would except from a specialised sensory molecule. We conclude that ISCA1 and CRY4, even if they do interact in vivo, are highly unlikely to form a functional protein biocompass.