diff --git a/concurrency-mapreduce/README.md b/concurrency-mapreduce/README.md
index 8fe76ce..1b385aa 100644
--- a/concurrency-mapreduce/README.md
+++ b/concurrency-mapreduce/README.md
@@ -143,6 +143,7 @@ infrastructure:
 ```
 #include <assert.h>
 #include <stdio.h>
+#include <stdlib.h>
 #include <string.h>
 #include "mapreduce.h"