diff --git a/vector.hpp b/vector.hpp
index 56725c66..b606f5bb 100644
--- a/vector.hpp
+++ b/vector.hpp
@@ -22,6 +22,7 @@
 
 #include "json.hpp"
 #include "detail/coord.hpp"
+#include "annotations.hpp"
 
 #include <array>
 #include <iostream>
@@ -70,8 +71,7 @@ namespace util {
         double dot (const util::vector<S>&) const;
 
         util::vector<S>& normalise  (void);
-        util::vector<S>  normalised (void) const;
-
+        util::vector<S>  normalised (void) const mustuse;
 
         bool is_zero (void) const;