diff --git a/include/proto/channel.h b/include/proto/channel.h
index 9e02dc0..3d8a1b7 100644
--- a/include/proto/channel.h
+++ b/include/proto/channel.h
@@ -134,7 +134,9 @@
  * end of transfer is close to happen. Note that both ->buf->o and ->to_forward
  * are considered as available since they're supposed to leave the buffer. The
  * test is optimized to avoid as many operations as possible for the fast case
- * and to be used as an "if" condition.
+ * and to be used as an "if" condition. Just like channel_recv_limit(), we
+ * never allow to overwrite the reserve until the output stream interface is
+ * connected, otherwise we could spin on a POST with http-send-name-header.
  */
 static inline int channel_full(const struct channel *chn)
 {
@@ -145,6 +147,9 @@
 	if (!rem)
 		return 1; /* buffer already full */
 
+	if (rem <= global.tune.maxrewrite && !channel_may_send(chn))
+		return 1;
+
 	/* now we know there's some room left, verify if we're touching
 	 * the reserve with some permanent input data.
 	 */