diff --git a/src/os_mac_conv.c b/src/os_mac_conv.c
index 3ede648..71960da 100644
--- a/src/os_mac_conv.c
+++ b/src/os_mac_conv.c
@@ -14,6 +14,8 @@
  */
 
 #define NO_X11_INCLUDES
+#define BalloonEval int   /* used in header files */
+
 #include "vim.h"
 #ifndef FEAT_GUI_MAC
 # include <CoreServices/CoreServices.h>