diff --git a/src/protocol/parser/pass_definitions.rs b/src/protocol/parser/pass_definitions.rs
index 94de9499c7f17bf17a73332551296924f9d7953d..144ae43b5ebb17aec83f692e1f76a28f78fca8e6 100644
--- a/src/protocol/parser/pass_definitions.rs
+++ b/src/protocol/parser/pass_definitions.rs
@@ -713,7 +713,10 @@ impl PassDefinitions {
             };
             consume_token(&module.source, iter, TokenKind::ArrowRight)?;
             let block = self.consume_block_or_wrapped_statement(module, iter, ctx)?;
-            cases.push(SelectCase{ guard, block });
+            cases.push(SelectCase{
+                guard, block,
+                involved_ports: Vec::with_capacity(1)
+            });
 
             next = iter.next();
         }