diff --git a/internal/protocol/protocol.go b/internal/protocol/protocol.go
index 048587b..af25a2c 100644
--- a/internal/protocol/protocol.go
+++ b/internal/protocol/protocol.go
@@ -90,6 +90,9 @@ type Service struct {
 	Digest        string `json:"digest,omitempty"`
 	Status        string `json:"status"`
 	Self          bool   `json:"self,omitempty"`
+	// Built says the Compose service has a build: section; it is never
+	// updated by jobs.
+	Built bool `json:"built,omitempty"`
 }
 
 // Key identifies the service within one agent's report. It is stable across