diff --git a/src/backend/backend.c b/src/backend/backend.c
index 9f67473..852c336 100644
--- a/src/backend/backend.c
+++ b/src/backend/backend.c
@@ -1,3 +1,5 @@
+// SPDX-License-Identifier: MPL-2.0
+// Copyright (c) Yuxuan Shui <yshuiv7@gmail.com>
 #include <xcb/xcb.h>
 
 #include "backend.h"
diff --git a/src/backend/backend_common.c b/src/backend/backend_common.c
index 96985b4..c6a1690 100644
--- a/src/backend/backend_common.c
+++ b/src/backend/backend_common.c
@@ -1,3 +1,5 @@
+// SPDX-License-Identifier: MPL-2.0
+// Copyright (c) Yuxuan Shui <yshuiv7@gmail.com>
 #include <string.h>
 #include <xcb/xcb_image.h>
 #include <xcb/render.h>
@@ -9,6 +11,7 @@
 #include "common.h"
 #include "log.h"
 #include "x.h"
+#include "win.h"
 
 /**
  * Generate a 1x1 <code>Picture</code> of a particular color.
diff --git a/src/backend/backend_common.h b/src/backend/backend_common.h
index 72321ab..b1ca686 100644
--- a/src/backend/backend_common.h
+++ b/src/backend/backend_common.h
@@ -1,4 +1,7 @@
+// SPDX-License-Identifier: MPL-2.0
+// Copyright (c) Yuxuan Shui <yshuiv7@gmail.com>
 #pragma once
+
 #include <xcb/render.h>
 #include <xcb/xcb_image.h>
 
diff --git a/src/backend/gl/gl_common.c b/src/backend/gl/gl_common.c
index a872c44..5ed4572 100644
--- a/src/backend/gl/gl_common.c
+++ b/src/backend/gl/gl_common.c
@@ -1,3 +1,5 @@
+// SPDX-License-Identifier: MPL-2.0
+// Copyright (c) Yuxuan Shui <yshuiv7@gmail.com>
 #include <GL/gl.h>
 #include <GL/glext.h>
 #include <locale.h>
diff --git a/src/backend/gl/gl_common.h b/src/backend/gl/gl_common.h
index 96ec047..c177cd8 100644
--- a/src/backend/gl/gl_common.h
+++ b/src/backend/gl/gl_common.h
@@ -1,3 +1,5 @@
+// SPDX-License-Identifier: MPL-2.0
+// Copyright (c) Yuxuan Shui <yshuiv7@gmail.com>
 #pragma once
 #include <stdbool.h>
 #include <string.h>
diff --git a/src/backend/gl/glx.c b/src/backend/gl/glx.c
index 52a64b1..ecec54c 100644
--- a/src/backend/gl/glx.c
+++ b/src/backend/gl/glx.c
@@ -5,6 +5,7 @@
  * Based on `xcompmgr` - Copyright (c) 2003, Keith Packard
  *
  * Copyright (c) 2011-2013, Christopher Jeffrey
+ * Copyright (c) 2019 Yuxuan Shui <yshuiv7@gmail.com>
  * See LICENSE-mit for more information.
  *
  */
diff --git a/src/backend/gl/glx.h b/src/backend/gl/glx.h
index df9b32c..a83603b 100644
--- a/src/backend/gl/glx.h
+++ b/src/backend/gl/glx.h
@@ -1,3 +1,5 @@
+// SPDX-License-Identifier: MPL-2.0
+// Copyright (c) Yuxuan Shui <yshuiv7@gmail.com>
 #pragma once
 #include <GL/glx.h>
 #include <X11/Xlib.h>
diff --git a/src/backend/xrender.c b/src/backend/xrender.c
index 321bf4c..fb2b258 100644
--- a/src/backend/xrender.c
+++ b/src/backend/xrender.c
@@ -1,3 +1,5 @@
+// SPDX-License-Identifier: MPL-2.0
+// Copyright (c) Yuxuan Shui <yshuiv7@gmail.com>
 #include <assert.h>
 #include <math.h>
 #include <stdlib.h>