--- a/examples/c/rpcalc/rpcalc.y
+++ b/examples/c/rpcalc/rpcalc.y
@@ -22,6 +22,7 @@
 
 %{
   #include <stdio.h>
+  #include <stdlib.h>
   #include <math.h>
   int yylex (void);
   void yyerror (char const *);