diff --git a/src/x11/app.cpp b/src/x11/app.cpp
index 6520be3a91..a788e7ee01 100644
--- a/src/x11/app.cpp
+++ b/src/x11/app.cpp
@@ -468,7 +468,7 @@ bool wxApp::ProcessXEvent(WXEvent* _event)
 
     win = wxGetWindowFromTable(window);
     if (!win)
-	    return;
+	    return FALSE;
 
 #ifdef __WXDEBUG__
     wxString windowClass = win->GetClassInfo()->GetClassName();