diff --git a/src/msw/app.cpp b/src/msw/app.cpp
index f1cdf6d385..703871214c 100644
--- a/src/msw/app.cpp
+++ b/src/msw/app.cpp
@@ -548,7 +548,7 @@ wxApp::~wxApp()
 // wxApp idle handling
 // ----------------------------------------------------------------------------
 
-void wxApp::OnIdle(wxIdleEvent& event)
+void wxApp::OnIdle(wxIdleEvent& WXUNUSED(event))
 {
 #if wxUSE_DC_CACHEING
     // automated DC cache management: clear the cached DCs and bitmap