On the JET facility, the line-integrated electron density is measured by a multichannel far-infrared (FIR) interferometer. The basic source of radiation is a deuterium cyanide (DCN) laser (λ = 195μm) measuring the density along four vertical and four lateral channels. During high-density discharge the system suffers from fringe jumps that are manually partially corrected by an off-line program. This intermittent phenomenon prevents reliable usage of the measured line-integrated density in a real-time feedback controller. To solve this problem we have developed a method to correct on the lateral channels in real-time the fringe jumps. The method uses the additional Alcohol laser (λ = 118.8μm) interferometer present on the lateral channels to compensate the vibrations. The method has been successfully tested with off-line test data, before implementation on a VME system for the real time control of the JET discharges.