diff --git a/src/mac/carbon/window.cpp b/src/mac/carbon/window.cpp
index 148538256d..7d4ce35592 100644
--- a/src/mac/carbon/window.cpp
+++ b/src/mac/carbon/window.cpp
@@ -108,6 +108,8 @@ void wxRemoveMacWindowAssociation(wxWindow *win)
 // constructors and such
 // ----------------------------------------------------------------------------
 
+WindowRef wxWindow::s_macWindowInUpdate = NULL;
+
 void wxWindow::Init()
 {
     // generic
diff --git a/src/mac/window.cpp b/src/mac/window.cpp
index 148538256d..7d4ce35592 100644
--- a/src/mac/window.cpp
+++ b/src/mac/window.cpp
@@ -108,6 +108,8 @@ void wxRemoveMacWindowAssociation(wxWindow *win)
 // constructors and such
 // ----------------------------------------------------------------------------
 
+WindowRef wxWindow::s_macWindowInUpdate = NULL;
+
 void wxWindow::Init()
 {
     // generic