diff --git a/dtc.h b/dtc.h
index 51c03ef..bb769d2 100644
--- a/dtc.h
+++ b/dtc.h
@@ -108,6 +108,8 @@
 	for_each_marker(m) \
 		if ((m)->type == (t))
 
+size_t type_marker_length(struct marker *m);
+
 void data_free(struct data d);
 
 struct data data_grow_for(struct data d, int xlen);
diff --git a/treesource.c b/treesource.c
index 53e6203..f2874f1 100644
--- a/treesource.c
+++ b/treesource.c
@@ -145,7 +145,7 @@
 	return m;
 }
 
-static size_t type_marker_length(struct marker *m)
+size_t type_marker_length(struct marker *m)
 {
 	struct marker *next = next_type_marker(m->next);