Size Exclusion Chromatography (SEC) of lignin poses many challenges. In numerous studies chromatograms of lignin show a bimodal molar mass distribution. Is this a true characteristic of lignin, is it caused by molecular associations or aggregations, or could it could be an artefact from using column combinations with porosities that do not match properly? To improve resolution and enable separation over a larger molar mass range, multiple columns with different porosities are often connected in series. If the porosities do not match properly, the result appears as a shoulder or bimodality in the chromatogram. To understand whether the bimodal distribution is a sample characteristic or an analyze artefact, we have used different columns, column combination and samples to see when the results is a bimodal distribution and when only one peak is formed. Results show that the bimodality of lignin can be an artifact originating from column mismatch. Using single porosity columns with a low molar mass cut-off should be avoided since it can cause false bimodality.