Make build work for plan9
diff --git a/termsize.go b/termsize.go
index 014881c..a144a71 100644
--- a/termsize.go
+++ b/termsize.go
@@ -1,4 +1,4 @@
-// +build !windows
+// +build !windows,!plan9
 
 package flags
 
diff --git a/termsize_windows.go b/termsize_nosysioctl.go
similarity index 70%
rename from termsize_windows.go
rename to termsize_nosysioctl.go
index 7583a3d..bdcac37 100644
--- a/termsize_windows.go
+++ b/termsize_nosysioctl.go
@@ -1,3 +1,5 @@
+// +build windows plan9
+
 package flags
 
 func getTerminalColumns() int {