diff --git a/swaylock/main.c b/swaylock/main.c
index b5ce63ef..a0a2f1cb 100644
--- a/swaylock/main.c
+++ b/swaylock/main.c
@@ -11,6 +11,7 @@
 #include <getopt.h>
 #include <signal.h>
 #include <stdbool.h>
+#include <unistd.h>
 
 #include "client/window.h"
 #include "client/registry.h"