diff --git a/fs/os_plan9.go b/fs/os_plan9.go
index 8819013..a75c57e 100644
--- a/fs/os_plan9.go
+++ b/fs/os_plan9.go
@@ -15,11 +15,22 @@ func createLockFile(name string, perm os.FileMode) (LockFile, bool, error) {
 	}
 	f, err := os.OpenFile(name, os.O_RDWR|os.O_CREATE, syscall.DMEXCL|perm)
 	if err != nil {
+		if acquiredExisting {
+			// Assume a recognizable error.
+			err = os.ErrExist
+		}
 		return nil, false, err
 	}
 	return &osLockFile{f, name}, acquiredExisting, nil
 }
 
+func (f *osLockFile) Unlock() (err error) {
+	if err = f.Close(); err == nil {
+		 err = os.Remove(f.path)
+	}
+	return
+}
+
 // Return a default FileSystem for this platform.
 func DefaultFileSystem() FileSystem {
 	return OS