diff --git a/layer2/CifFile.cpp b/layer2/CifFile.cpp
index b53785b95..50adbae37 100644
--- a/layer2/CifFile.cpp
+++ b/layer2/CifFile.cpp
@@ -10,6 +10,7 @@
 #include <stdlib.h>
 #include <string.h>
 
+#include <algorithm>
 #include <cassert>
 #include <iostream>
 #include <numeric>