diff --git a/alloc/arena.hpp b/alloc/arena.hpp
index a61939bb..16be21dd 100644
--- a/alloc/arena.hpp
+++ b/alloc/arena.hpp
@@ -23,6 +23,8 @@
 #include <utility>
 
 namespace util::alloc {
+    /// wraps a block allocator with an interface suitable for allocating
+    /// individual objects.
     template <class T>
     class arena {
     public: