1 files changed, 2 insertions, 0 deletions
diff --git a/delta.h b/delta.h
index 727ae30e9..7b3f86d85 100644
--- a/delta.h
+++ b/delta.h
@@ -18,6 +18,8 @@ create_delta_index(const void *buf, unsigned long bufsize);
 
 /*
  * free_delta_index: free the index created by create_delta_index()
+ *
+ * Given pointer must be what create_delta_index() returned, or NULL.
  */
 extern void free_delta_index(struct delta_index *index);