diff --git a/src/headers/tomcrypt.h b/src/headers/tomcrypt.h
index da5e4f9..3b4232b 100644
--- a/src/headers/tomcrypt.h
+++ b/src/headers/tomcrypt.h
@@ -4,6 +4,7 @@
 #include <stdio.h>
 #include <string.h>
 #include <stdlib.h>
+#include <stddef.h>
 #include <time.h>
 #include <ctype.h>
 #include <limits.h>