Building panels provided with a locking system for vertical locking of a first and a second building panel by a vertical displacement of the second building panel against the first building panel, the building panels comprising: a sidewardly open tongue groove provided at an edge of the first building panel; a strip protruding below the tongue groove and outwardly beyond an upper part of the edge of said first building panel, the strip comprising a locking element configured to cooperate with a downwardly open locking groove formed on the second building panel for locking of the first and the second building panels (1,1') in a horizontal direction; and a displaceable tongue provided in a sidewardly open displacement groove at an edge of the second building panel, the displaceable tongue comprising a main body extending along the edge of the second building panel and a tongue locking surface located at an upper and outer part of the tongue, the tongue locking surface being configured to cooperate with a groove locking surface of the tongue groove for vertical locking, wherein the displaceable tongue comprises an inner part spaced inwardly from an upper part of the edge of said second building panel, and the inner part comprises a tongue pressing surface configured to cooperate with a strip pressing surface on the strip such that the displaceable tongue is displaced into the tongue groove when the tongue pressing surface and the strip pressing surface are displaced vertically against each other to obtain a locking of the first and the second building panels (1,1') in a vertical direction, characterised in that said displaceable tongue comprises a protrusion and the second panel comprises a cavity for housing the protrusion, the tongue pressing surface being provided on the protrusion and the strip pressing surface being provided on the locking element, and the protrusion comprises a part that is flexible. a sidewardly open tongue groove provided at an edge of the first building panel; a strip protruding below the tongue groove and outwardly beyond an upper part of the edge of said first building panel, the strip comprising a locking element configured to cooperate with a downwardly open locking groove formed on the second building panel for locking of the first and the second building panels (1,1') in a horizontal direction; and a displaceable tongue provided in a sidewardly open displacement groove at an edge of the second building panel, the displaceable tongue comprising a main body extending along the edge of the second building panel and a tongue locking surface located at an upper and outer part of the tongue, the tongue locking surface being configured to cooperate with a groove locking surface of the tongue groove for vertical locking, wherein the displaceable tongue comprises an inner part spaced inwardly from an upper part of the edge of said second building panel, and the inner part comprises a tongue pressing surface configured to cooperate with a strip pressing surface on the strip such that the displaceable tongue is displaced into the tongue groove when the tongue pressing surface and the strip pressing surface are displaced vertically against each other to obtain a locking of the first and the second building panels (1,1') in a vertical direction, characterised in that said displaceable tongue comprises a protrusion and the second panel comprises a cavity for housing the protrusion, the tongue pressing surface being provided on the protrusion and the strip pressing surface being provided on the locking element, and the protrusion comprises a part that is flexible.