diff --git a/include/wx/font.h b/include/wx/font.h
index dd1665ab0a..dae2cc4f76 100644
--- a/include/wx/font.h
+++ b/include/wx/font.h
@@ -31,6 +31,7 @@
 class WXDLLEXPORT wxFontData;
 class WXDLLEXPORT wxFontBase;
 class WXDLLEXPORT wxFont;
+class WXDLLEXPORT wxSize;
 
 // ----------------------------------------------------------------------------
 // font constants