diff --git a/src/modules/systemlib/param/param.c b/src/modules/systemlib/param/param.c
index 9f9d146025..726d9f457d 100644
--- a/src/modules/systemlib/param/param.c
+++ b/src/modules/systemlib/param/param.c
@@ -157,7 +157,7 @@ static void param_set_used_internal(param_t param);
 
 static param_t param_find_internal(const char *name, bool notification);
 
-static px4_sem_t param_sem;
+static px4_sem_t param_sem; ///< this protects against concurrent access to param_values and param save
 
 /** lock the parameter store */
 static void
diff --git a/src/modules/systemlib/param/param_shmem.c b/src/modules/systemlib/param/param_shmem.c
index fcf46d699b..d6a42fbe29 100644
--- a/src/modules/systemlib/param/param_shmem.c
+++ b/src/modules/systemlib/param/param_shmem.c
@@ -165,7 +165,7 @@ static void param_set_used_internal(param_t param);
 
 static param_t param_find_internal(const char *name, bool notification);
 
-static px4_sem_t param_sem;
+static px4_sem_t param_sem; ///< this protects against concurrent access to param_values and param save
 
 /** lock the parameter store */
 static void