diff --git a/include/cyclone/runtime.h b/include/cyclone/runtime.h
index 52c90ef7..052ac076 100644
--- a/include/cyclone/runtime.h
+++ b/include/cyclone/runtime.h
@@ -442,6 +442,7 @@ object Cyc_has_cycle(object lst);
 object Cyc_is_boolean(object o);
 #define Cyc_is_pair(o) ((is_object_type(o) && ((list) o)->tag == pair_tag) ? boolean_t : boolean_f)
 #define Cyc_is_null(o) make_boolean(o == NULL)
+TODO: convert all of these to macros (if it makes sense, most should), and remove them from runtime.c:
 object Cyc_is_number(object o);
 object Cyc_is_complex(object o);
 object Cyc_is_real(object o);