diff -up ClanLib-2.3.7/Sources/API/GL/opengl_defines.h~ ClanLib-2.3.7/Sources/API/GL/opengl_defines.h
--- ClanLib-2.3.7/Sources/API/GL/opengl_defines.h~	2012-01-31 14:05:43.000000000 +0100
+++ ClanLib-2.3.7/Sources/API/GL/opengl_defines.h	2019-02-12 20:03:50.318693860 +0100
@@ -68,8 +68,6 @@ typedef double GLdouble;
 typedef double GLclampd;
 typedef void GLvoid;
 typedef char GLchar;
-typedef ptrdiff_t GLintptr;
-typedef ptrdiff_t GLsizeiptr;
 typedef struct __CLsync *CLsync;
 
 typedef void * CLDEBUGPROCARB;
diff -up ClanLib-2.3.7/Sources/API/GL1/opengl1_defines.h~ ClanLib-2.3.7/Sources/API/GL1/opengl1_defines.h
--- ClanLib-2.3.7/Sources/API/GL1/opengl1_defines.h~	2013-01-15 16:23:53.000000000 +0100
+++ ClanLib-2.3.7/Sources/API/GL1/opengl1_defines.h	2019-02-12 23:09:29.268058408 +0100
@@ -64,8 +64,6 @@ typedef double GLdouble;
 typedef double GLclampd;
 typedef void GLvoid;
 typedef char GLchar;
-typedef ptrdiff_t GLintptr;
-typedef ptrdiff_t GLsizeiptr;
 
 #else
 typedef unsigned long GLenum;