diff --git a/config/default.nix b/config/default.nix
index 8afc9716..c8ab51a3 100644
--- a/config/default.nix
+++ b/config/default.nix
@@ -13,6 +13,11 @@
       assertion = lib.versions.major pkgs.ceph.version != 16;
       message = "Please pin ceph to major version 16!";
     }
+    {
+      assertion = lib.versions.majorMinor pkgs.mediawiki.version != 1.39;
+      # https://www.mediawiki.org/wiki/Version_lifecycle
+      message = "Please keep mediawiki on LTS versions which is required by the LDAP extension";
+    }
   ];
 
   boot = {