diff --git a/tools/testing/selftests/filesystems/statmount/statmount_test.c b/tools/testing/selftests/filesystems/statmount/statmount_test.c
index 3eafd7da58e2..e6d7c4f1c85b 100644
--- a/tools/testing/selftests/filesystems/statmount/statmount_test.c
+++ b/tools/testing/selftests/filesystems/statmount/statmount_test.c
@@ -3,6 +3,7 @@
 #define _GNU_SOURCE
 
 #include <assert.h>
+#include <stddef.h>
 #include <stdint.h>
 #include <sched.h>
 #include <fcntl.h>