diff --git a/cli/error_plan9.go b/cli/error_plan9.go
new file mode 100644
index 0000000000000000000000000000000000000000..aa04fe3f42b982e6ef66895f0616a46d68828779
--- /dev/null
+++ b/cli/error_plan9.go
@@ -0,0 +1,15 @@
+package cli
+
+import "syscall"
+
+func isErrnoNotSupported(err error) bool {
+	switch err {
+	case
+		// Operation not supported
+		syscall.EINVAL, syscall.EPLAN9,
+		// Sync on os.Stdin or os.Stderr returns "permission denied".
+		syscall.EPERM:
+		return true
+	}
+	return false
+}
diff --git a/cli/error_posix.go b/cli/error_posix.go
index d2d6b2bb6d89528523358f3f6fdf612fd7705a0f..7ab44166d45350a74f8c0568f5d42f24d6f9d1c8 100644
--- a/cli/error_posix.go
+++ b/cli/error_posix.go
@@ -1,4 +1,4 @@
-//+build !windows
+//+build !windows,!plan9
 
 package cli