diff --git a/timestamp.hh b/timestamp.hh
index e77344e598..46586e3a1a 100644
--- a/timestamp.hh
+++ b/timestamp.hh
@@ -24,6 +24,7 @@
 #include <cstdint>
 #include <limits>
 #include <chrono>
+#include <string>
 #include "clocks-impl.hh"
 
 namespace api {