diff --git a/src/runtime/error.rs b/src/runtime/error.rs
index 231fa8a7e0d0794c4cac69f1bb886e6d478407e9..409d56d590d11d1e3fa2256275f917b7b72f6204 100644
--- a/src/runtime/error.rs
+++ b/src/runtime/error.rs
@@ -15,6 +15,7 @@ pub enum ConnectError {
 }
 #[derive(Eq, PartialEq, Copy, Clone, Debug)]
 pub enum AddComponentError {
+    DuplicatePort(PortId),
     NoSuchComponent,
     NonPortTypeParameters,
     CannotMovePort(PortId),