diff --git a/agents/linux.nix b/agents/linux.nix
index 3bf16d2..546f0f1 100644
--- a/agents/linux.nix
+++ b/agents/linux.nix
@@ -29,6 +29,9 @@ in {
   users.users.gitea-runner.extraGroups = [ "docker" ];
   users.users.gitea-runner.isNormalUser = true;
 
+  # Runner communication port for cache restores.
+  networking.firewall.allowedTCPPorts = [ 45315 ];
+
   services.gitea-actions-runner = {
     package = pkgs.forgejo-actions-runner;
     instances.default = {