diff --git a/src/transport.c b/src/transport.c
index 19efdf2..6e1349d 100644
--- a/src/transport.c
+++ b/src/transport.c
@@ -587,6 +587,10 @@ send_existing(LIBSSH2_SESSION * session, unsigned char *data,
 
     /* send as much as possible of the existing packet */
     if ((data != p->odata) || (data_len != p->olen)) {
+        if (data != p->odata)
+            _libssh2_debug(session, LIBSSH2_DBG_TRANS, "data!=p->odata");
+        if (data_len != p->olen)
+            _libssh2_debug(session, LIBSSH2_DBG_TRANS, "data_len!=p->olen");
         /* When we are about to complete the sending of a packet, it is vital
            that the caller doesn't try to send a new/different packet since
            we don't add this one up until the previous one has been sent. To