diff --git a/RELEASE-NOTES.md b/RELEASE-NOTES.md
index d2ffdf25..72247f07 100644
--- a/RELEASE-NOTES.md
+++ b/RELEASE-NOTES.md
@@ -16,6 +16,8 @@ Please report any bugs and incompatibilities in
     represents the shadow frame buffer of the screen. 
     * configure option: `--enable-syncupdate`
     * macro: `_MGUSE_SYNC_UPDATE`
+  1. New API: `UpdateInvalidClient`. You can use this function to update
+    the invalid client region of a window instantly.
   1. Use different colors for the output of `_DBG_PRINTF` and `_ERR_PRINTF`.
   1. Add `__mg_save_jpg` function for storing MYBITMAP as JPEG file (10km).
   1. Modified logic for checking JPEG format (10km).
diff --git a/include/window.h b/include/window.h
index 1b812d06..8c2dae99 100644
--- a/include/window.h
+++ b/include/window.h
@@ -5338,6 +5338,22 @@ MG_EXPORT void GUIAPI DumpWindow (FILE* fp, HWND hWnd);
  */
 MG_EXPORT void GUIAPI UpdateWindow (HWND hWnd, BOOL bErase);
 
+/**
+ * \fn void GUIAPI UpdateInvalidClient (HWND hWnd, BOOL bErase)
+ * \brief Updates the invalid client areas in a window.
+ *
+ * This function updates the client areas specified by \a hWnd.
+ * It will redraw the invalid client area of the window, and 
+ * if \b bErase is TRUE, the client area will be erased by using 
+ * background color.
+ *
+ * \param hWnd The handle to the window.
+ * \param bErase Indicates whether to erase the client area of the window.
+ *
+ * \sa UpdateWindow
+ */
+MG_EXPORT void GUIAPI UpdateInvalidClient (HWND hWnd, BOOL bErase);
+
 /**
  * \fn BOOL GUIAPI ShowWindow (HWND hWnd, int iCmdShow)
  * \brief Shows or hides a window.
diff --git a/src/gui/window.c b/src/gui/window.c
index 0c4b37bd..37b10c15 100644
--- a/src/gui/window.c
+++ b/src/gui/window.c
@@ -3977,8 +3977,7 @@ void GUIAPI UpdateWindow (HWND hWnd, BOOL fErase)
 #endif
 }
 
-MG_EXPORT void GUIAPI UpdateInvalidRect (HWND hWnd, BOOL bErase);
-void GUIAPI UpdateInvalidRect (HWND hWnd, BOOL fErase)
+void GUIAPI UpdateInvalidClient (HWND hWnd, BOOL fErase)
 {
     MG_CHECK (MG_IS_NORMAL_WINDOW(hWnd));