diff --git a/dlls/user32/controls.h b/dlls/user32/controls.h
index 35be6450739..2df4f450cb7 100644
--- a/dlls/user32/controls.h
+++ b/dlls/user32/controls.h
@@ -38,6 +38,7 @@ enum builtin_winprocs
     WINPROC_DIALOG,
     WINPROC_EDIT,
     WINPROC_LISTBOX,
+    WINPROC_MDICLIENT,
     WINPROC_SCROLLBAR,
     WINPROC_STATIC,
     NB_BUILTIN_WINPROCS
diff --git a/dlls/user32/mdi.c b/dlls/user32/mdi.c
index e1910f85aac..fcfbd27e001 100644
--- a/dlls/user32/mdi.c
+++ b/dlls/user32/mdi.c
@@ -150,8 +150,6 @@ static LONG MDI_ChildActivate( HWND, HWND );
 static LRESULT MDI_RefreshMenu(MDICLIENTINFO *);
 
 static HWND MDI_MoreWindowsDialog(HWND);
-static LRESULT WINAPI MDIClientWndProcA( HWND hwnd, UINT message, WPARAM wParam, LPARAM lParam );
-static LRESULT WINAPI MDIClientWndProcW( HWND hwnd, UINT message, WPARAM wParam, LPARAM lParam );
 
 /* -------- Miscellaneous service functions ----------
  *
@@ -188,8 +186,8 @@ const struct builtin_class_descr MDICLIENT_builtin_class =
 {
     mdiclientW,             /* name */
     0,                      /* style */
-    MDIClientWndProcA,      /* procA */
-    MDIClientWndProcW,      /* procW */
+    NULL,                  /* procA */
+    BUILTIN_WINPROC(WINPROC_MDICLIENT), /* procW */
     sizeof(MDICLIENTINFO),  /* extra */
     IDC_ARROW,              /* cursor */
     (HBRUSH)(COLOR_APPWORKSPACE+1)    /* brush */
@@ -1271,24 +1269,6 @@ LRESULT MDIClientWndProc_common( HWND hwnd, UINT message, WPARAM wParam, LPARAM
                      DefWindowProcA( hwnd, message, wParam, lParam );
 }
 
-/***********************************************************************
- *		MDIClientWndProcA
- */
-static LRESULT WINAPI MDIClientWndProcA( HWND hwnd, UINT message, WPARAM wParam, LPARAM lParam )
-{
-    if (!IsWindow(hwnd)) return 0;
-    return wow_handlers.mdiclient_proc( hwnd, message, wParam, lParam, FALSE );
-}
-
-/***********************************************************************
- *		MDIClientWndProcW
- */
-static LRESULT WINAPI MDIClientWndProcW( HWND hwnd, UINT message, WPARAM wParam, LPARAM lParam )
-{
-    if (!IsWindow(hwnd)) return 0;
-    return wow_handlers.mdiclient_proc( hwnd, message, wParam, lParam, TRUE );
-}
-
 /***********************************************************************
  *		DefFrameProcA (USER32.@)
  */
diff --git a/dlls/user32/winproc.c b/dlls/user32/winproc.c
index 89a1ae98126..d71dca2d3e5 100644
--- a/dlls/user32/winproc.c
+++ b/dlls/user32/winproc.c
@@ -57,6 +57,8 @@ LRESULT WINAPI EditWndProcA( HWND hwnd, UINT msg, WPARAM wParam, LPARAM lParam )
 static LRESULT WINAPI EditWndProcW( HWND hwnd, UINT msg, WPARAM wParam, LPARAM lParam );
 static LRESULT WINAPI ListBoxWndProcA( HWND hwnd, UINT msg, WPARAM wParam, LPARAM lParam );
 static LRESULT WINAPI ListBoxWndProcW( HWND hwnd, UINT msg, WPARAM wParam, LPARAM lParam );
+static LRESULT WINAPI MDIClientWndProcA( HWND hwnd, UINT msg, WPARAM wParam, LPARAM lParam );
+static LRESULT WINAPI MDIClientWndProcW( HWND hwnd, UINT msg, WPARAM wParam, LPARAM lParam );
 static LRESULT WINAPI ScrollBarWndProcA( HWND hwnd, UINT msg, WPARAM wParam, LPARAM lParam );
 static LRESULT WINAPI ScrollBarWndProcW( HWND hwnd, UINT msg, WPARAM wParam, LPARAM lParam );
 static LRESULT WINAPI StaticWndProcA( HWND hwnd, UINT msg, WPARAM wParam, LPARAM lParam );
@@ -69,6 +71,7 @@ static WINDOWPROC winproc_array[MAX_WINPROCS] =
     { DefDlgProcA, DefDlgProcW },              /* WINPROC_DIALOG */
     { EditWndProcA, EditWndProcW },            /* WINPROC_EDIT */
     { ListBoxWndProcA, ListBoxWndProcW },      /* WINPROC_LISTBOX */
+    { MDIClientWndProcA, MDIClientWndProcW },  /* WINPROC_MDICLIENT */
     { ScrollBarWndProcA, ScrollBarWndProcW },  /* WINPROC_SCROLLBAR */
     { StaticWndProcA, StaticWndProcW },        /* WINPROC_STATIC */
 };
@@ -1096,6 +1099,16 @@ static LRESULT WINAPI ListBoxWndProcW( HWND hwnd, UINT msg, WPARAM wParam, LPARA
     return wow_handlers.listbox_proc( hwnd, msg, wParam, lParam, TRUE );
 }
 
+static LRESULT WINAPI MDIClientWndProcA( HWND hwnd, UINT msg, WPARAM wParam, LPARAM lParam )
+{
+    return wow_handlers.mdiclient_proc( hwnd, msg, wParam, lParam, FALSE );
+}
+
+static LRESULT WINAPI MDIClientWndProcW( HWND hwnd, UINT msg, WPARAM wParam, LPARAM lParam )
+{
+    return wow_handlers.mdiclient_proc( hwnd, msg, wParam, lParam, TRUE );
+}
+
 static LRESULT WINAPI ScrollBarWndProcA( HWND hwnd, UINT msg, WPARAM wParam, LPARAM lParam )
 {
     return wow_handlers.scrollbar_proc( hwnd, msg, wParam, lParam, FALSE );