diff --git a/nixos/modules/tasks/network-interfaces-systemd.nix b/nixos/modules/tasks/network-interfaces-systemd.nix
index 70158fc7252b..8223c5a4941e 100644
--- a/nixos/modules/tasks/network-interfaces-systemd.nix
+++ b/nixos/modules/tasks/network-interfaces-systemd.nix
@@ -35,7 +35,10 @@ in
     assertions = [ {
       assertion = cfg.defaultGatewayWindowSize == null;
       message = "networking.defaultGatewayWindowSize is not supported by networkd.";
-    } ];
+    } ] ++ flip mapAttrsToList cfg.bridges (n: { rstp, ... }: {
+      assertion = !rstp;
+      message = "networking.bridges.${n}.rstp is not supported by networkd.";
+    });
 
     systemd.services.dhcpcd.enable = mkDefault false;