diff --git a/cruft/util/concepts.hpp b/cruft/util/concepts.hpp
index 65dd727b..af9f9359 100644
--- a/cruft/util/concepts.hpp
+++ b/cruft/util/concepts.hpp
@@ -53,13 +53,19 @@ namespace cruft::concepts {
 
 
     /// Anything that can be looped over using begin/end
+    ///
+    /// We don't check end against legacy_iterator because that won't work for std::default_sentinel.
+    /// Rather, the important part is that it's equality comparable against whatever std::begin returns.
     template <typename T>
     concept iterable = requires (T t)
     {
         { std::begin  (t) } -> named::legacy_iterator;
-        { std::end    (t) } -> named::legacy_iterator;
+        std::begin (t) == std::end (t);
+        std::begin (t) != std::end (t);
+
         { std::cbegin (t) } -> named::legacy_iterator;
-        { std::cend   (t) } -> named::legacy_iterator;
+        std::cbegin (t) == std::cend (t);
+        std::cbegin (t) != std::cend (t);
     };