diff --git a/src/msw/treectrl.cpp b/src/msw/treectrl.cpp
index 08f8e0779f..e9bfaa8961 100644
--- a/src/msw/treectrl.cpp
+++ b/src/msw/treectrl.cpp
@@ -293,7 +293,7 @@ class wxTreeItemParam
 {
 public:
     wxTreeItemParam()
-        : m_item(NULL),
+        : m_item((void*)NULL),
           m_data(NULL)
     {
         for ( size_t n = 0; n < WXSIZEOF(m_images); n++ )