diff --git a/commit.h b/commit.h
index 6d857f0..baecc0a 100644
--- a/commit.h
+++ b/commit.h
@@ -247,7 +247,7 @@ struct commit_graft {
 };
 typedef int (*each_commit_graft_fn)(const struct commit_graft *, void *);
 
-struct commit_graft *read_graft_line(char *buf, int len);
+struct commit_graft *read_graft_line(struct strbuf *line);
 int register_commit_graft(struct commit_graft *, int);
 struct commit_graft *lookup_commit_graft(const struct object_id *oid);