Add missing include files
diff --git a/archival/libunarchive/data_extract_to_stdout.c b/archival/libunarchive/data_extract_to_stdout.c
index d4137a1..df2bca6 100644
--- a/archival/libunarchive/data_extract_to_stdout.c
+++ b/archival/libunarchive/data_extract_to_stdout.c
@@ -15,6 +15,7 @@
  */
 
 #include "unarchive.h"
+#include <unistd.h>
 
 extern void data_extract_to_stdout(archive_handle_t *archive_handle)
 {