diff --git a/datetime.cc b/datetime.cc
index d766e00c..0a5f5440 100644
--- a/datetime.cc
+++ b/datetime.cc
@@ -8,6 +8,7 @@
 #include <ctime>
 #include <cctype>
 #include <climits>
+#include <cstdlib>
 
 date_t       date_t::now(std::time(NULL));
 int	     date_t::current_year = date_t::now.year();
diff --git a/option.cc b/option.cc
index af9c8a59..bc173e84 100644
--- a/option.cc
+++ b/option.cc
@@ -6,6 +6,7 @@
 
 #include <iostream>
 #include <cstdarg>
+#include <cstdlib>
 #include <unistd.h>
 
 #include "util.h"