diff --git a/src/sw_sup/setup_build_pc.md b/src/sw_sup/setup_build_pc.md
index 714ca34..9ca0c7b 100644
--- a/src/sw_sup/setup_build_pc.md
+++ b/src/sw_sup/setup_build_pc.md
@@ -33,7 +33,13 @@ by Vivado.
        }
     }
     ```
-4. Enable flakes in Nix by e.g. adding `experimental-features = nix-command flakes` to nix.conf (for example `~/.config/nix/nix.conf`).
+4. Enable flakes in Nix and add `/opt` to sandbox e.g. adding following to the `nix.conf` (for example `~/.config/nix/nix.conf` or `/etc/nix/nix.conf`):
+    ```
+    experimental-features = nix-command flakes
+    extra-sandbox-paths = /opt
+    ```
+5. On Ubuntu, the Nix will conflict with Apparmor. You'll need to disable Apparmor for Nix, 
+   or for the whole system (you can also delete Apparmor completely, but be careful with it).
 
 From here, you should be able to enter ARTIQ development shell directly from URL, or by cloning the repository.
 The later will allow you to edit the source code in case of need.