diff --git a/include/xo/arena/DArenaHashMap.hpp b/include/xo/arena/DArenaHashMap.hpp
index e560bdb..c20695e 100644
--- a/include/xo/arena/DArenaHashMap.hpp
+++ b/include/xo/arena/DArenaHashMap.hpp
@@ -68,7 +68,7 @@ namespace xo {
             struct HashMapStore : DArenaHashMapUtil {
             public:
                 using value_type = std::pair<const Key, Value>;
-                using group_type = detail::Group;
+                using group_type = detail::ControlGroup;
 
             public:
                 /** group_exp2: number of groups {x, 2^x} **/
@@ -264,7 +264,7 @@ namespace xo {
             using key_hash = Hash;
             using key_equal = Equal;
             using byte = std::byte;
-            using group_type = detail::Group;
+            using group_type = detail::ControlGroup;
             using store_type = detail::HashMapStore<Key, Value>;
             using insert_value_type = std::pair<value_type *, bool>;
             using iterator = detail::DArenaHashMapIterator<Key, Value>;
diff --git a/include/xo/arena/hashmap/ControlGroup.hpp b/include/xo/arena/hashmap/ControlGroup.hpp
index 2b60a79..d5db66a 100644
--- a/include/xo/arena/hashmap/ControlGroup.hpp
+++ b/include/xo/arena/hashmap/ControlGroup.hpp
@@ -17,10 +17,11 @@ namespace xo {
              *
              *  Support optimization using SIMD operations
              **/
-            struct Group {
+            struct ControlGroup {
                 std::array<uint8_t, DArenaHashMapUtil::c_group_size> ctrl_;
 
-                explicit Group(uint8_t * lo) {
+                /** Require: lo is aligned on c_group_size (probably 16 bytes) **/
+                explicit ControlGroup(uint8_t * lo) {
                     ::memcpy(ctrl_.data(), lo, DArenaHashMapUtil::c_group_size);
                 }