diff --git a/src/internal.h b/src/internal.h
index bd4c53078..a21375c9f 100644
--- a/src/internal.h
+++ b/src/internal.h
@@ -104,6 +104,7 @@ typedef const GLubyte* (APIENTRY * PFNGLGETSTRINGPROC)(GLenum);
 typedef void (APIENTRY * PFNGLGETINTEGERVPROC)(GLenum,GLint*);
 typedef const GLubyte* (APIENTRY * PFNGLGETSTRINGIPROC)(GLenum,GLuint);
 
+#if !defined(VULKAN_H_)
 #define VK_NULL_HANDLE 0
 
 typedef void* VkInstance;
@@ -171,6 +172,8 @@ typedef void (APIENTRY * PFN_vkVoidFunction)(void);
   #define vkGetInstanceProcAddr _glfw.vk.GetInstanceProcAddr
 #endif
 
+#endif //VULKAN_H_
+
 #if defined(_GLFW_COCOA)
  #include "cocoa_platform.h"
 #elif defined(_GLFW_WIN32)