--- a/calc.yy	2011-05-18 12:26:38.701666366 +0200
+++ b/calc.yy	2011-05-18 12:27:43.020672135 +0200
@@ -17,7 +17,7 @@
 #include "formula.h"
 #include "formula-variables.h"
 
-int yyerror(char* s);
+int yyerror(const char* s);
 int yylex();
 
 const char* yyinStr;
@@ -149,7 +149,7 @@
 	return c;
 }
 
-int yyerror(char* s) {
+int yyerror(const char* s) {
 	printf("yyerror: %s\n", s);
 	return 0;
 }