diff --git a/src/buffers.c b/src/buffers.c
index 44b3f7d..43c0647 100644
--- a/src/buffers.c
+++ b/src/buffers.c
@@ -196,7 +196,7 @@
 		return 0;
 
 	/* OK so the data fits in the buffer in one or two blocks */
-	max = buffer_contig_space_with_len(buf, max);
+	max = buffer_contig_space_with_res(buf, buf->size - max);
 	memcpy(buf->r, blk, MIN(len, max));
 	if (len > max)
 		memcpy(buf->data, blk + max, len - max);