diff --git a/src/fundamental/sha256.h b/src/fundamental/sha256.h
index 4805cc553a..dbb08e35e5 100644
--- a/src/fundamental/sha256.h
+++ b/src/fundamental/sha256.h
@@ -1,6 +1,7 @@
 /* SPDX-License-Identifier: LGPL-2.1-or-later */
 #pragma once
 
+#include <stddef.h>
 #include <stdint.h>
 
 #define SHA256_DIGEST_SIZE 32