diff -up ClanLib-1.0.0/Sources/API/Core/System/cl_assert.h~ ClanLib-1.0.0/Sources/API/Core/System/cl_assert.h
--- ClanLib-1.0.0/Sources/API/Core/System/cl_assert.h~ 2006-10-27 03:55:01.000000000 +0200
+++ ClanLib-1.0.0/Sources/API/Core/System/cl_assert.h 2018-05-29 14:54:12.132106898 +0200
@@ -33,6 +33,8 @@
#ifndef header_cl_assert
#define header_cl_assert
+#include <cstddef>
+
#ifdef CL_API_DLL
#ifdef CL_CORE_EXPORT
#define CL_API_CORE __declspec(dllexport)