diff --git a/include/GLFW/glfw3.h b/include/GLFW/glfw3.h
index 68d005dd..9259f55e 100644
--- a/include/GLFW/glfw3.h
+++ b/include/GLFW/glfw3.h
@@ -117,10 +117,9 @@ extern "C" {
 
 /* Most Windows GLU headers need wchar_t.
  * The OS X OpenGL header blocks the definition of ptrdiff_t by glext.h.
+ * Include it unconditionally to avoid surprising side-effects.
  */
-#if !defined(GLFW_INCLUDE_NONE)
- #include <stddef.h>
-#endif
+#include <stddef.h>
 
 /* Include the chosen client API headers.
  */
diff --git a/src/internal.h b/src/internal.h
index 48488233..cbc04828 100644
--- a/src/internal.h
+++ b/src/internal.h
@@ -47,8 +47,6 @@
 #define GLFW_INCLUDE_NONE
 #include "../include/GLFW/glfw3.h"
 
-#include <stddef.h>
-
 #if defined(_MSC_VER) && (_MSC_VER < 1600)
 typedef unsigned __int64 GLFWuint64;
 #else