diff --git a/CXX/yapi.hh b/CXX/yapi.hh
index 65d9ec4b8..167ad2bf6 100644
--- a/CXX/yapi.hh
+++ b/CXX/yapi.hh
@@ -23,6 +23,7 @@
 extern "C" {
 
 #include <stddef.h>
+#ifdef __cplusplus
 #define old_cplusplus __cplusplus
 #undef __cplusplus
 #endif