diff --git a/src/backend.c b/src/backend.c
index 75792bd..17a55d6 100644
--- a/src/backend.c
+++ b/src/backend.c
@@ -313,6 +313,9 @@
 	if (len == 0)
 		return NULL;
 
+	if (len > req->buf->data + req->buf->size - p)
+		len = req->buf->data + req->buf->size - p;
+
 	if (px->lbprm.tot_weight == 0)
 		return NULL;