diff --git a/src/internal.h b/src/internal.h
index fc57f364f..0ffc7c12c 100644
--- a/src/internal.h
+++ b/src/internal.h
@@ -94,6 +94,7 @@ 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;
@@ -155,6 +156,8 @@ typedef VkResult (APIENTRY * PFN_vkEnumerateInstanceExtensionProperties)(const c
 #define vkEnumerateInstanceExtensionProperties _glfw.vk.EnumerateInstanceExtensionProperties
 #define vkGetInstanceProcAddr _glfw.vk.GetInstanceProcAddr
 
+#endif //VULKAN_H_
+
 #if defined(_GLFW_COCOA)
  #include "cocoa_platform.h"
 #elif defined(_GLFW_WIN32)