diff --git a/nix/buildkite/default.nix b/nix/buildkite/default.nix
index d96801361..d229e9885 100644
--- a/nix/buildkite/default.nix
+++ b/nix/buildkite/default.nix
@@ -17,7 +17,6 @@ let
     foldl'
     hasAttr
     hashString
-    isNull
     isString
     length
     listToAttrs