diff --git a/nix/nixos-module/container/bird.nix b/nix/nixos-module/container/bird.nix
index 2a84dad..8aefc32 100644
--- a/nix/nixos-module/container/bird.nix
+++ b/nix/nixos-module/container/bird.nix
@@ -116,14 +116,14 @@ in
                   # Enable OSPF only on networks with a secret. Others
                   # are treated as a stubnet whose routes to
                   # advertise.
-                  if config.site.net ? net && config.site.net.${net}.ospf.secret != null
+                  if config.site.net ? "${net}" && config.site.net.${net}.ospf.secret != null
                   then ''
                     interface "${net}" {
                       authentication cryptographic;
                       password "${config.site.net.${net}.ospf.secret}";
                     };
                   ''
-                  else if config.site.net ? net && config.site.net.${net}.subnet4 != null
+                  else if config.site.net ? "${net}" && config.site.net.${net}.subnet4 != null
                   then ''
                     # Advertise route of network ${net}
                     stubnet ${config.site.net.${net}.subnet4} {};