diff --git a/config/default.nix b/config/default.nix
index 58b50cbd..8afc9716 100644
--- a/config/default.nix
+++ b/config/default.nix
@@ -9,6 +9,10 @@
       assertion = config.system.replaceRuntimeDependencies == [];
       message = "system.replaceRuntimeDependencies causes hydra to build the system at evaluation time. It must be removed!";
     }
+    {
+      assertion = lib.versions.major pkgs.ceph.version != 16;
+      message = "Please pin ceph to major version 16!";
+    }
   ];
 
   boot = {