diff --git a/include/wx/wx.h b/include/wx/wx.h
index fb2696046d..5abb78f5a3 100644
--- a/include/wx/wx.h
+++ b/include/wx/wx.h
@@ -89,12 +89,19 @@
 #include "wx/combobox.h"
 #include "wx/layout.h"
 #include "wx/sizer.h"
-#include "wx/mdi.h"
 #include "wx/statusbr.h"
 #include "wx/choicdlg.h"
 #include "wx/textdlg.h"
 #include "wx/filedlg.h"
 
+// this one is included by exactly one file (mdi.cpp) during wx build so even
+// although we keep it here for the library users, don't include it to avoid
+// bloating the PCH and (worse) rebuilding the entire library when it changes
+// when building the library itself
+#ifndef WXBUILDING
+    #include "wx/mdi.h"
+#endif
+
 // always include, even if !wxUSE_VALIDATORS because we need wxDefaultValidator
 #include "wx/validate.h"