diff --git a/src/generic/splitter.cpp b/src/generic/splitter.cpp
index 1d6a539568..58ec6da0e3 100644
--- a/src/generic/splitter.cpp
+++ b/src/generic/splitter.cpp
@@ -662,7 +662,7 @@ void wxSplitterWindow::SizeWindows()
 // Set pane for unsplit window
 void wxSplitterWindow::Initialize(wxWindow *window)
 {
-    wxASSERT_MSG( window && window->GetParent() == this,
+    wxASSERT_MSG( (!window || (window && window->GetParent() == this)),
                   _T("windows in the splitter should have it as parent!") );
 
     m_windowOne = window;