diff --git a/krebs/4lib/default.nix b/krebs/4lib/default.nix
index deac02bb7..e984614a0 100644
--- a/krebs/4lib/default.nix
+++ b/krebs/4lib/default.nix
@@ -17,7 +17,7 @@ let out = rec {
 
   types = import ./types.nix {
     inherit config;
-    lib = lib // { inherit genid; };
+    lib = lib // { inherit genid optionalTrace; };
   };
 
   dir.has-default-nix = path: pathExists (path + "/default.nix");
@@ -44,4 +44,6 @@ let out = rec {
   mapAttrValues = f: mapAttrs (_: f);
   setAttr = name: value: set: set // { ${name} = value; };
 
+  optionalTrace = c: msg: x: if c then trace msg x else x;
+
 }; in out