diff --git a/src/channel.c b/src/channel.c
index 125037076..2f983960d 100644
--- a/src/channel.c
+++ b/src/channel.c
@@ -174,7 +174,7 @@ int bi_putblk(struct channel *chn, const char *blk, int len)
 		return 0;
 
 	/* OK so the data fits in the buffer in one or two blocks */
-	max = buffer_contig_space_with_res(chn->buf, chn->buf->size - max);
+	max = buffer_contig_space(chn->buf);
 	memcpy(bi_end(chn->buf), blk, MIN(len, max));
 	if (len > max)
 		memcpy(chn->buf->data, blk + max, len - max);