diff --git a/src/runtime2/inbox.rs b/src/runtime2/inbox.rs
index 808fe06a90cb43fb4205329a7104e634a10e41b5..f1175db78a17bb428cdee71c3bf0cc6c8d43210a 100644
--- a/src/runtime2/inbox.rs
+++ b/src/runtime2/inbox.rs
@@ -22,6 +22,7 @@ pub(crate) struct PortAnnotation {
 pub(crate) struct SyncHeader {
     pub sending_component_id: ConnectorId,
     pub highest_component_id: ConnectorId,
+    pub sync_round: u32,
 }
 
 /// The header added to data messages