diff --git a/src/x509_helper_log.cc b/src/x509_helper_log.cc
index 588791e..d99fd5d 100644
--- a/src/x509_helper_log.cc
+++ b/src/x509_helper_log.cc
@@ -14,6 +14,7 @@
 #include <cstdio>
 #include <cstdlib>
 #include <cstring>
+#include <ctime>
 
 using namespace std;  // NOLINT