diff --git a/include/types/trace.h b/include/types/trace.h
index e43cb88..152cc8f 100644
--- a/include/types/trace.h
+++ b/include/types/trace.h
@@ -129,6 +129,9 @@
 	const char *desc;
 	const struct trace_event *known_events;
 	struct list source_link; // element in list of known trace sources
+	void (*default_cb)(enum trace_level level, uint64_t mask,
+	                   const struct trace_source *src, const struct ist where,
+	                   const void *a1, const void *a2, const void *a3, const void *a4);
 	uint32_t arg_def;        // argument definitions (sum of TRC_ARG{1..4}_*)
 	const struct trace_lockon_arg *lockon_args; // must be 4 entries if not NULL
 	/* trace configuration, adjusted by "trace <module>" on CLI */