diff --git a/libao2/pl_format.c b/libao2/pl_format.c
index 168cdeb0dd..f4c5876422 100644
--- a/libao2/pl_format.c
+++ b/libao2/pl_format.c
@@ -7,6 +7,7 @@
 
 #include <stdio.h>
 #include <stdlib.h>
+#include <unistd.h>
 
 #include "audio_out.h"
 #include "audio_plugin.h"