diff --git a/vector.cpp b/vector.cpp
index 407a47f5..57a82877 100644
--- a/vector.cpp
+++ b/vector.cpp
@@ -181,6 +181,11 @@ util::vector<S,T>::is_zero (void) const
 
 
 //-----------------------------------------------------------------------------
+template <size_t S, typename T>
+const util::vector<S,T>
+util::vector<S,T>::UNIT (T{1});
+
+
 template <size_t S, typename T>
 const util::vector<S,T>
 util::vector<S,T>::ZERO (T{0});
diff --git a/vector.hpp b/vector.hpp
index d85e570e..20c405a3 100644
--- a/vector.hpp
+++ b/vector.hpp
@@ -43,6 +43,7 @@ namespace util {
         vector<S,T>  normalised [[gnu::warn_unused_result]] (void) const;
 
         // constants
+        static const vector<S,T> UNIT;
         static const vector<S,T> ZERO;
 
         void sanity (void) const;