diff --git a/src/channel.c b/src/channel.c
index b3382a7..c5a51f7 100644
--- a/src/channel.c
+++ b/src/channel.c
@@ -151,7 +151,7 @@
 		return -3;
 
 	max = channel_recv_limit(chn);
-	if (unlikely(len > max - buffer_len(chn->buf))) {
+	if (unlikely(len > max - b_data(chn->buf))) {
 		/* we can't write this chunk right now because the buffer is
 		 * almost full or because the block is too large. Return the
 		 * available space or -2 if impossible.