diff --git a/cpp/opengl/render_context.hpp b/cpp/opengl/render_context.hpp
index 8e8ff74..43409c4 100644
--- a/cpp/opengl/render_context.hpp
+++ b/cpp/opengl/render_context.hpp
@@ -17,10 +17,12 @@
 #define _RK_ENGINE_RENDER_CONTEXT_H
 
 #include "../render.hpp"
-#include <GL/glx.h>
 
-extern PFNGLDRAWELEMENTSINSTANCEDBASEINSTANCEPROC rk_DrawElementsInstancedBaseInstance;
-extern PFNGLMULTIDRAWELEMENTSINDIRECTPROC rk_MultiDrawElementsIndirect;
+typedef void (*rk_DrawElementsInstancedBaseInstanceFunc)(rk_uint, rk_uint, rk_uint, const void *, rk_uint, rk_uint);
+typedef void (*rk_MultiDrawElementsIndirectFunc)(rk_uint, rk_uint, const void *, rk_uint, rk_uint);
+
+extern rk_DrawElementsInstancedBaseInstanceFunc rk_DrawElementsInstancedBaseInstance;
+extern rk_MultiDrawElementsIndirectFunc rk_MultiDrawElementsIndirect;
 
 extern rk_window_t rk_create_context(
     char const * name,
diff --git a/cpp/opengl/render_context_glx.cpp b/cpp/opengl/render_context_glx.cpp
index 92f8920..99d54bd 100644
--- a/cpp/opengl/render_context_glx.cpp
+++ b/cpp/opengl/render_context_glx.cpp
@@ -21,6 +21,7 @@
 #include <cstring>
 #include <GLES3/gl32.h>
 #include <X11/Xlib.h>
+#include <GL/glx.h>
 
 extern unsigned rk_events_mask;
 
@@ -35,8 +36,8 @@ static bool rk_error_occured = false;
 #define GLX_CONTEXT_MINOR_VERSION_ARB 0x2092
 typedef GLXContext (*glXCreateContextAttribsARBProc)(Display *, GLXFBConfig, GLXContext, Bool, int const *);
 
-PFNGLDRAWELEMENTSINSTANCEDBASEINSTANCEPROC rk_DrawElementsInstancedBaseInstance = nullptr;
-PFNGLMULTIDRAWELEMENTSINDIRECTPROC rk_MultiDrawElementsIndirect = nullptr;
+rk_DrawElementsInstancedBaseInstanceFunc rk_DrawElementsInstancedBaseInstance = nullptr;
+rk_MultiDrawElementsIndirectFunc rk_MultiDrawElementsIndirect = nullptr;
 
 static int const rk_visual_attribs[] = {
     GLX_X_RENDERABLE, True,
@@ -202,13 +203,13 @@ rk_window_t rk_create_context(
     char const * const gl_exts = reinterpret_cast<char const *>(glGetString(GL_EXTENSIONS));
     if (rk_extension_supported(gl_exts, "GL_EXT_base_instance")) {
         rk_DrawElementsInstancedBaseInstance =
-            reinterpret_cast<PFNGLDRAWELEMENTSINSTANCEDBASEINSTANCEPROC>(
+            reinterpret_cast<rk_DrawElementsInstancedBaseInstanceFunc>(
                 glXGetProcAddressARB(reinterpret_cast<GLubyte const *>("DrawElementsInstancedBaseInstance")));
         if (rk_DrawElementsInstancedBaseInstance) {
             rk_printf("Using extension GL_EXT_base_instance::DrawElementsInstancedBaseInstance.");
             if (rk_extension_supported(gl_exts, "GL_EXT_multi_draw_indirect")) {
                 rk_MultiDrawElementsIndirect =
-                    reinterpret_cast<PFNGLMULTIDRAWELEMENTSINDIRECTPROC>(
+                    reinterpret_cast<rk_MultiDrawElementsIndirectFunc>(
                         glXGetProcAddressARB(reinterpret_cast<GLubyte const *>("MultiDrawElementsIndirectEXT")));
                 if (rk_MultiDrawElementsIndirect) {
                     rk_printf("Using extension GL_EXT_multi_draw_indirect::MultiDrawElementsIndirectEXT.");