diff --git a/proxy/proxy.c b/proxy/proxy.c
index 6bedcf9b..801c28f9 100644
--- a/proxy/proxy.c
+++ b/proxy/proxy.c
@@ -232,6 +232,13 @@ static void proxy_negotiate(ProxySocket *ps)
                                 ps->proxy_nodelay, ps->proxy_keepalive,
                                 &ps->plugimpl);
         ps->pn->reconnect = false;
+        /* If the negotiator has asked us to reconnect, they are
+         * expecting that on the next call their input queue will
+         * consist entirely of data from the _new_ connection, without
+         * any remaining data buffered from the old one. (If they'd
+         * wanted the latter, they could have read it out of the input
+         * queue before asking us to close the connection.) */
+        bufchain_clear(&ps->pending_input_data);
     }
 
     while (bufchain_size(&ps->output_from_negotiator)) {