diff --git a/src/event/MultiSocketMonitor.cxx b/src/event/MultiSocketMonitor.cxx
index b5114cfb3..f22b0a022 100644
--- a/src/event/MultiSocketMonitor.cxx
+++ b/src/event/MultiSocketMonitor.cxx
@@ -20,6 +20,8 @@
 #include "config.h"
 #include "MultiSocketMonitor.hxx"
 
+#include <algorithm>
+
 #ifndef WIN32
 #include <poll.h>
 #endif