diff --git a/src/cmd/gc/go.h b/src/cmd/gc/go.h
index 2459e538ec4..ad2dd48ffe3 100644
--- a/src/cmd/gc/go.h
+++ b/src/cmd/gc/go.h
@@ -667,6 +667,7 @@ struct	Magic
 };
 
 typedef struct	Prog Prog;
+#pragma incomplete Prog
 
 struct	Label
 {