diff --git a/lib/flake_env__util.re b/lib/flake_env__util.re
index 2d9c062..e05c1fa 100644
--- a/lib/flake_env__util.re
+++ b/lib/flake_env__util.re
@@ -3,7 +3,7 @@ module Unix = Core_unix;
 
 let nix = (args) => {
   let stdout_chan = Unix.open_process_in(
-    "nix --extra-experimental-features \"nix-command flakes\" " ++ (args |> String.concat));
+    "nix --extra-experimental-features \"nix-command flakes\" " ++ (args |> String.concat(~sep=" ")));
   let stdout_content = stdout_chan |> In_channel.input_all;
   let exit_code = Unix.close_process_in(stdout_chan);
   (exit_code, stdout_content)