diff --git a/src/udev/udevd.c b/src/udev/udevd.c
index 018a3cd6e7..8f0e5cc0d6 100644
--- a/src/udev/udevd.c
+++ b/src/udev/udevd.c
@@ -5,6 +5,8 @@
  * Copyright © 2009 Scott James Remnant <scott@netsplit.com>
  */
 
+#include <unistd.h>
+
 #include "errno-util.h"
 #include "fd-util.h"
 #include "mkdir.h"