diff --git a/examples/configuration.nix b/examples/configuration.nix
index fa12f8c..7d4ff87 100644
--- a/examples/configuration.nix
+++ b/examples/configuration.nix
@@ -45,7 +45,7 @@
   ### LND
   # Disable clightning and uncomment the following line in order to enable lnd,
   # a lightning implementation written in Go.
-  # services.lnd.enable = assert (!config.services.clightning.enable); true;
+  # services.lnd.enable = true;
   ## WARNING
   # If you use lnd, you should manually backup your wallet mnemonic
   # seed. This will allow you to recover on-chain funds. You can run the
diff --git a/modules/modules.nix b/modules/modules.nix
index faf12a7..93774c4 100644
--- a/modules/modules.nix
+++ b/modules/modules.nix
@@ -26,6 +26,15 @@
   };
 
   config = {
+    assertions = [
+      # lnd.wantedBy == [] needed for `test/tests.nix` in which both clightning and lnd are enabled
+      { assertion = config.services.lnd.enable -> (!config.services.clightning.enable || config.systemd.services.lnd.wantedBy == []);
+        message = ''
+          LND and clightning can't be run in parallel because they both bind to lightning port 9735.
+        '';
+      }
+    ];
+
     nixpkgs.overlays = [ (self: super: {
       nix-bitcoin = let
         pkgs = import ../pkgs { pkgs = super; };