diff --git a/README.md b/README.md
index 00e4c5c7..f31e14b5 100644
--- a/README.md
+++ b/README.md
@@ -64,6 +64,7 @@ GLFW bundles a number of dependencies in the `deps/` directory.
 
  - [Cocoa] Bugfix: `glfwSetWindowSize` did not change the video mode for full
                    screen windows
+ - [X11] Added support for Cygwin-X
  - [X11] Made XInput2 optional at compile-time
  - [X11] Made Xxf86vm optional at compile-time
 
diff --git a/src/x11_init.c b/src/x11_init.c
index dc33bcee..8a00eb84 100644
--- a/src/x11_init.c
+++ b/src/x11_init.c
@@ -587,7 +587,7 @@ static GLboolean initExtensions(void)
     detectEWMH();
 
     // Find or create string format atoms
-    _glfw.x11._NULL = XInternAtom(_glfw.x11.display, "NULL", False);
+    _glfw.x11.NULL_ = XInternAtom(_glfw.x11.display, "NULL", False);
     _glfw.x11.UTF8_STRING =
         XInternAtom(_glfw.x11.display, "UTF8_STRING", False);
     _glfw.x11.COMPOUND_STRING =
diff --git a/src/x11_platform.h b/src/x11_platform.h
index 0c6450b3..22bb7e0d 100644
--- a/src/x11_platform.h
+++ b/src/x11_platform.h
@@ -160,7 +160,7 @@ typedef struct _GLFWlibraryX11
     Atom            CLIPBOARD;
     Atom            CLIPBOARD_MANAGER;
     Atom            SAVE_TARGETS;
-    Atom            _NULL;
+    Atom            NULL_;
     Atom            UTF8_STRING;
     Atom            COMPOUND_STRING;
     Atom            ATOM_PAIR;
diff --git a/src/x11_window.c b/src/x11_window.c
index 77a34597..359c7d45 100644
--- a/src/x11_window.c
+++ b/src/x11_window.c
@@ -28,6 +28,7 @@
 #include "internal.h"
 
 #include <X11/cursorfont.h>
+#include <X11/Xmd.h>
 
 #include <sys/select.h>
 
@@ -632,7 +633,7 @@ static Atom writeTargetToProperty(const XSelectionRequestEvent* request)
         XChangeProperty(_glfw.x11.display,
                         request->requestor,
                         request->property,
-                        _glfw.x11._NULL,
+                        _glfw.x11.NULL_,
                         32,
                         PropModeReplace,
                         NULL,
@@ -1739,7 +1740,7 @@ void _glfwPlatformPostEmptyEvent(void)
     event.type = ClientMessage;
     event.xclient.window = window->x11.handle;
     event.xclient.format = 32; // Data is 32-bit longs
-    event.xclient.message_type = _glfw.x11._NULL;
+    event.xclient.message_type = _glfw.x11.NULL_;
 
     XSendEvent(_glfw.x11.display, window->x11.handle, False, 0, &event);
     XFlush(_glfw.x11.display);