diff --git a/src/shrpx_connection_handler.h b/src/shrpx_connection_handler.h
index 1f9986af..c45c7462 100644
--- a/src/shrpx_connection_handler.h
+++ b/src/shrpx_connection_handler.h
@@ -32,6 +32,7 @@
 #include <sys/socket.h>
 #endif // HAVE_SYS_SOCKET_H
 
+#include <mutex>
 #include <memory>
 #include <vector>
 #include <random>