diff --git a/cmd/merge_zips/merge_zips.go b/cmd/merge_zips/merge_zips.go
index 27179cb..a9be612 100644
--- a/cmd/merge_zips/merge_zips.go
+++ b/cmd/merge_zips/merge_zips.go
@@ -417,7 +417,7 @@
 	}
 	oldOlderMiz := miz.older
 	if oldOlderMiz.newer != miz {
-		panic(fmt.Errorf("broken list between %p:%#v and %p:%#v", miz, oldOlderMiz))
+		panic(fmt.Errorf("broken list between %p:%#v and %p:%#v", miz, miz, oldOlderMiz, oldOlderMiz))
 	}
 	miz.older = olderMiz
 	olderMiz.older = oldOlderMiz