diff --git a/lib/default.nix b/lib/default.nix
index 280f04299..187514a30 100644
--- a/lib/default.nix
+++ b/lib/default.nix
@@ -45,6 +45,8 @@ let
     genid_uint31 = x: ((lib.genid_uint32 x) + 16777216) / 2;
     genid_uint32 = import ./genid.nix { inherit lib; };
 
+    hexchars = stringToCharacters "0123456789abcdef";
+
     lpad = n: c: s:
       if lib.stringLength s < n
         then lib.lpad n c (c + s)
diff --git a/lib/genid.nix b/lib/genid.nix
index 0aed1d351..bfa4a9a03 100644
--- a/lib/genid.nix
+++ b/lib/genid.nix
@@ -32,6 +32,5 @@ let out = genid;
   hexint = x: hexvals.${toLower x};
 
   # :: attrset char uint4
-  hexvals = listToAttrs (imap (i: c: { name = c; value = i - 1; })
-                        (stringToCharacters "0123456789abcdef"));
+  hexvals = listToAttrs (imap (i: c: { name = c; value = i - 1; }) hexchars);
 in out