diff --git a/lib/c/test/test_labcomm_copy.c b/lib/c/test/test_labcomm_copy.c
index 9b9a0fd709a8eed0be8acdfbe9b893b342806816..b7b5e0829b01a6ad98306fbf56263bbdca61d6e5 100644
--- a/lib/c/test/test_labcomm_copy.c
+++ b/lib/c/test/test_labcomm_copy.c
@@ -2,6 +2,7 @@
 #include <stdio.h>
 #include <sys/types.h>
 #include <sys/stat.h>
+#include <unistd.h>
 #include <fcntl.h>
 #include <assert.h>
 #include <err.h>