An electrochemical, measuring probe, for measuring a chemical or physical, measured variable, of a measured medium, wherein the measuring probe comprises: at least one measuring half cell and at least one reference half cell, and the reference half cell includes: a housing of electrically insulating material, in which a reference electrolyte chamber containing a liquid, reference electrolyte is formed, and which has in a housing wall a diaphragm permeable for the reference electrolyte for providing electrolytic contact between the reference half cell and the measured medium; a potential indicating element extending into the reference electrolyte; and a supply opening opening into the reference electrolyte chamber for supply of reference electrolyte into the reference electrolyte chamber. The reference half cell has a check valve blocking exit of reference electrolyte from the reference electrolyte chamber through the supply opening, especially a check valve arranged at least partially within the supply opening.