diff --git a/cmake/xo_cxx.cmake b/cmake/xo_cxx.cmake
index f0e2e29b..13ee6b9a 100644
--- a/cmake/xo_cxx.cmake
+++ b/cmake/xo_cxx.cmake
@@ -108,6 +108,14 @@ macro(xo_add_shared_library target targetversion soversion sources)
     xo_install_library2(${target})
 endmacro()
 
+# ----------------------------------------------------------------
+# use this for a header-only library
+#
+macro(xo_add_headeronly_library target)
+    add_library(${target} INTERFACE)
+    xo_include_headeronly_options2(${target})
+endmacro()
+
 # ----------------------------------------------------------------
 # use this in subdirs that compile c++ code.
 # do not use for header-only subsystems;  see xo_include_headeronly_options2()