diff --git a/libfreefare/felica.c b/libfreefare/felica.c
index f549119..443c595 100644
--- a/libfreefare/felica.c
+++ b/libfreefare/felica.c
@@ -13,6 +13,7 @@
 
 #include <assert.h>
 #include <errno.h>
+#include <stdlib.h>
 #include <string.h>
 
 #include <sys/types.h>