diff --git a/archival/libunarchive/seek_sub_file.c b/archival/libunarchive/seek_sub_file.c
index 76cc0bc0c..72a3754bc 100644
--- a/archival/libunarchive/seek_sub_file.c
+++ b/archival/libunarchive/seek_sub_file.c
@@ -17,6 +17,7 @@
 #include <stdio.h>
 #include <errno.h>
 #include <stdlib.h>
+#include <unistd.h>
 
 off_t archive_offset;