diff --git a/include/wx/msw/treectrl.h b/include/wx/msw/treectrl.h
index a2a86df75a..18df088b58 100644
--- a/include/wx/msw/treectrl.h
+++ b/include/wx/msw/treectrl.h
@@ -247,7 +247,7 @@ protected:
     // handle a key event in a multi-selection control
     //
     // return true if the key was processed, false otherwise
-    bool MSWHandleSelectionKey(WPARAM vkey);
+    bool MSWHandleSelectionKey(unsigned vkey);
 
 
     // data used only while editing the item label:
diff --git a/src/msw/treectrl.cpp b/src/msw/treectrl.cpp
index 72fa295d37..1f45e5b01e 100644
--- a/src/msw/treectrl.cpp
+++ b/src/msw/treectrl.cpp
@@ -2131,7 +2131,7 @@ bool wxTreeCtrl::MSWCommand(WXUINT cmd, WXWORD id_)
     return true;
 }
 
-bool wxTreeCtrl::MSWHandleSelectionKey(WPARAM vkey)
+bool wxTreeCtrl::MSWHandleSelectionKey(unsigned vkey)
 {
     const bool bCtrl = wxIsCtrlDown();
     const bool bShift = wxIsShiftDown();