diff --git a/.github/workflows/build.yml b/.github/workflows/build.yml
index b595c7e9..e1fd549e 100644
--- a/.github/workflows/build.yml
+++ b/.github/workflows/build.yml
@@ -13,6 +13,7 @@ jobs:
           - freebsd
           - ios
           - linux
+          - plan9
           - windows
         goarch:
           - amd64
diff --git a/fen.go b/fen.go
index b3ac3d8f..3836bf70 100644
--- a/fen.go
+++ b/fen.go
@@ -32,7 +32,7 @@ func (w *Watcher) Add(name string) error {
 	return nil
 }
 
-// Remove stops watching the the named file or directory (non-recursively).
+// Remove stops watching the named file or directory (non-recursively).
 func (w *Watcher) Remove(name string) error {
 	return nil
 }
diff --git a/kqueue.go b/kqueue.go
index 87c25b06..a93332fc 100644
--- a/kqueue.go
+++ b/kqueue.go
@@ -102,7 +102,7 @@ func (w *Watcher) Add(name string) error {
 	return err
 }
 
-// Remove stops watching the the named file or directory (non-recursively).
+// Remove stops watching the named file or directory (non-recursively).
 func (w *Watcher) Remove(name string) error {
 	name = filepath.Clean(name)
 	w.mu.Lock()
diff --git a/plan9.go b/plan9.go
new file mode 100644
index 00000000..0d9a87b3
--- /dev/null
+++ b/plan9.go
@@ -0,0 +1,36 @@
+// Copyright 2020 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+//go:build plan9
+// +build plan9
+
+package fsnotify
+
+import "syscall"
+
+// Watcher watches a set of files, delivering events to a channel.
+type Watcher struct {
+	Events chan Event
+	Errors chan error
+}
+
+// NewWatcher establishes a new watcher with the underlying OS and begins waiting for events.
+func NewWatcher() (*Watcher, error) {
+	return nil, syscall.EPLAN9
+}
+
+// Close removes all watches and closes the events channel.
+func (w *Watcher) Close() error {
+	return syscall.EPLAN9
+}
+
+// Add starts watching the named file or directory (non-recursively).
+func (w *Watcher) Add(name string) error {
+	return syscall.EPLAN9
+}
+
+// Remove stops watching the named file or directory (non-recursively).
+func (w *Watcher) Remove(name string) error {
+	return syscall.EPLAN9
+}
diff --git a/windows.go b/windows.go
index ecae0ce1..d3816609 100644
--- a/windows.go
+++ b/windows.go
@@ -92,7 +92,7 @@ func (w *Watcher) Add(name string) error {
 	return <-in.reply
 }
 
-// Remove stops watching the the named file or directory (non-recursively).
+// Remove stops watching the named file or directory (non-recursively).
 func (w *Watcher) Remove(name string) error {
 	in := &input{
 		op:    opRemoveWatch,