diff --git a/include/proto/action.h b/include/proto/action.h
index fea40cf..ce94aa0 100644
--- a/include/proto/action.h
+++ b/include/proto/action.h
@@ -68,4 +68,12 @@
 		*p = '\0';
 }
 
+/* for an action ACT_ACTION_TRK_SC*, return a tracking index starting at zero
+ * for SC0. Unknown actions also return zero.
+ */
+static inline int trk_idx(int trk_action)
+{
+	return trk_action - ACT_ACTION_TRK_SC0;
+}
+
 #endif /* _PROTO_ACTION_H */