diff --git a/src/unicode.cpp b/src/unicode.cpp
index 46650bff0..f4e941cd1 100644
--- a/src/unicode.cpp
+++ b/src/unicode.cpp
@@ -5,6 +5,7 @@
 #include "unicode.h"
 #include "unicode-data.h"
 
+#include <algorithm>
 #include <cassert>
 #include <cstddef>
 #include <cstdint>