diff --git a/src/hmtrp/hmtrp.h b/src/hmtrp/hmtrp.h
index 473ac1c9..1fd9c008 100644
--- a/src/hmtrp/hmtrp.h
+++ b/src/hmtrp/hmtrp.h
@@ -64,6 +64,7 @@ namespace upm {
    * configuration mode by grounding the CONFIG pin on the module.
    *
    * @ingroup grove uart radio
+   * @defgroup hmtrp libupm-hmtrp
    * @snippet hmtrp.cxx Interesting
    */
   class HMTRP {