--- a/parser/calc/main.c
+++ b/parser/calc/main.c
@@ -4,11 +4,13 @@
  */
 
 #include <stdio.h>
+#include <stdlib.h>
 
 extern int yyparse ();
 
 int main (int argc, char **argv)
 {
     yyparse ();
-    return 0;
+
+    return EXIT_SUCCESS;
 }