<p>The ESA Swarm constellation includes three satellites, which have been observing the Earth's ionosphere since November 2013, following polar orbits. The main ionospheric plasma parameters, such as electron density and temperature, are measured by means of Langmuir probes (Lps); electron density measurements, in particular, are nowadays largely considered as qualitatively reliable, and have been used in several published papers to date. In this work, we aim to discuss how some technical characteristics of Swarm Lps, such as their size and location on board the satellites, as well as the operational setup of the instruments, could lead to limitations in their accuracy if one underestimates the influence of satellite proximity, and the larger extension of the plasma sheath surrounding the probes due to the operational point of the voltage ripple. Two specific corrections are proposed for the assessment and possible mitigation of such effects. Finally, a comparison is made with electron density measurements from CSES-01 mission, which relies on Langmuir probes as well, whose geometry and operating mode are standard.</p>