diff --git a/check-fmt b/check-fmt
index 4c41da4..e3a5587 100755
--- a/check-fmt
+++ b/check-fmt
@@ -1,5 +1,5 @@
 #!/usr/bin/env nix-shell
-#!nix-shell -i bash
+#!nix-shell ./shell.nix -i bash
 #
 # Just because the nixpkgs-fmt error message is not super readable. Used by
 # CI.