diff --git a/src/beval.h b/src/beval.h
index 49ba05b..21900c5 100644
--- a/src/beval.h
+++ b/src/beval.h
@@ -76,6 +76,9 @@
     int			*vts;		// vartabstop setting for this buffer
 #endif
     char_u		*msg;
+#ifdef FEAT_GUI_W32
+    void		*tofree;
+#endif
 } BalloonEval;
 
 #define EVAL_OFFSET_X 15 /* displacement of beval topleft corner from pointer */