diff --git a/coord/base.hpp b/coord/base.hpp
index 4172e2d6..a8b37367 100644
--- a/coord/base.hpp
+++ b/coord/base.hpp
@@ -33,7 +33,7 @@ namespace util { namespace coord {
         static constexpr size_t dimension = S;
         static constexpr size_t elements = S;
 
-        size_t size (void) const { return S; }
+        constexpr size_t size (void) const { return S; }
 
         // constructors
         using init<S,T,tags...>::init;