diff --git a/src/units.hh b/src/units.hh
index ff4ed882..3bdfe253 100644
--- a/src/units.hh
+++ b/src/units.hh
@@ -5,6 +5,7 @@
 #include "hash.hh"
 
 #include <type_traits>
+#include <compare>
 
 namespace Kakoune
 {