Volcanic rocks are considered reliable recorders of past changes in the Earth’s magnetic field. Recent flows, however, sometimes fail to produce the known magnetic field at the time of cooling. Here, we tested the accuracy of paleomagnetic data recorded by Mt. Etna lavas by comparing paleomagnetic data from historical flows to direct measurements of the magnetic field above the current topography. The inclinations and intensities in both data sets are biased towards lower values. They vary as a function of topography; both are higher above ridges and lower in gullies. To suppress this paleomagnetic data bias it is important to take samples several meters apart and from different parts of the flow whenever possible. While this leads to a higher degree of scatter in paleodirections, the results will better represent the Earth’s magnetic field at the time of cooling. This emphasises the importance of reporting paleomagnetic sampling strategies in detail.