--- ./sql/sql_yacc.cc.orig	2019-10-08 16:31:04.000000000 +0200
+++ ./sql/sql_yacc.cc	2019-10-08 16:31:04.000000000 +0200
@@ -215,7 +215,7 @@
      The result will be in the process stderr (var/log/master.err)
    */
 
-  extern int yydebug;
+  static int yydebug;
   yydebug= 1;
 }
 #endif
--- ./sql/sql_yacc.yy.orig	2019-10-08 16:31:05.000000000 +0200
+++ ./sql/sql_yacc.yy	2019-10-08 16:31:04.000000000 +0200
@@ -169,7 +169,7 @@
      The result will be in the process stderr (var/log/master.err)
    */
 
-  extern int yydebug;
+  static int yydebug;
   yydebug= 1;
 }
 #endif