diff --git a/CMakeLists.txt b/CMakeLists.txt
index 3127d7ae..51cf7907 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -77,6 +77,7 @@ set(DOX_EXCLUDE_PATTERNS [=[
 add_subdirectory(xo-cmake)
 add_subdirectory(xo-indentlog)
 add_subdirectory(xo-reflectutil)  # header-only reflect support
+add_subdirectory(xo-arena)   # arena allocator (DArena)
 add_subdirectory(xo-facet)   # sep iface,data
 add_subdirectory(xo-allocutil)
 add_subdirectory(xo-refcnt)