diff --git a/src/h3.c b/src/h3.c
index 85eca90d7..987dc053b 100644
--- a/src/h3.c
+++ b/src/h3.c
@@ -93,7 +93,8 @@ static inline size_t h3_decode_frm_header(uint64_t *ftype, uint64_t *flen,
 	return hlen;
 }
 
-/* Decode <qcs> remotely initiated bidi-stream.
+/* Decode <qcs> remotely initiated bidi-stream. <fin> must be set to indicate
+ * that we received the last data of the stream.
  * Returns <0 on error else 0.
  */
 static int h3_decode_qcs(struct qcs *qcs, int fin, void *ctx)