diff --git a/test/sigchld.go b/test/sigchld.go
index a60d28deaa..9024f39956 100644
--- a/test/sigchld.go
+++ b/test/sigchld.go
@@ -1,4 +1,4 @@
-// +build !windows
+// +build !windows !plan9
 // cmpout
 
 // Copyright 2009 The Go Authors. All rights reserved.