diff --git a/data/c++.m4 b/data/c++.m4
index 000902ee..07899bd8 100644
--- a/data/c++.m4
+++ b/data/c++.m4
@@ -278,7 +278,7 @@ m4_define([b4_symbol_type_declare],
       location_type location;])[
 
     private:
-#if !defined __cplusplus || __cplusplus < 201103L
+#if YY_CPLUSPLUS < 201103L
       /// Assignment operator.
       basic_symbol& operator= (const basic_symbol& other);
 #endif