diff --git a/lib/src/upper/rlc_tm.cc b/lib/src/upper/rlc_tm.cc
index 14cfe37ea..e006072c6 100644
--- a/lib/src/upper/rlc_tm.cc
+++ b/lib/src/upper/rlc_tm.cc
@@ -153,7 +153,7 @@ int rlc_tm::read_pdu(uint8_t *payload, uint32_t nof_bytes)
 {
   uint32_t pdu_size = ul_queue.size_tail_bytes();
   if (pdu_size > nof_bytes) {
-    log->error("TX %s PDU size larger than MAC opportunity\n", rrc->get_rb_name(lcid).c_str());
+    log->error("TX %s PDU size larger than MAC opportunity (%d > %d)\n", rrc->get_rb_name(lcid).c_str(), pdu_size, nof_bytes);
     return -1;
   }
   byte_buffer_t *buf;
diff --git a/lib/src/upper/rlc_um.cc b/lib/src/upper/rlc_um.cc
index 4fee0e7b6..24e66389c 100644
--- a/lib/src/upper/rlc_um.cc
+++ b/lib/src/upper/rlc_um.cc
@@ -774,6 +774,11 @@ void rlc_um::rlc_um_rx::reassemble_rx_sdus()
       if (rx_sdu->N_bytes == 0 && i == 0 && !rlc_um_start_aligned(rx_window[vr_ur].header.fi)) {
         log->warning_hex(rx_window[vr_ur].buf->msg, len, "Dropping first %d B of SN %d due to lost start segment\n", len, vr_ur);
 
+        if (rx_window[vr_ur].buf->N_bytes < len) {
+          log->error("Dropping remaining remainder of SN %d too (N_bytes=%u < len=%d)\n", vr_ur, rx_window[vr_ur].buf->N_bytes, len);
+          goto clean_up_rx_window;
+        }
+
         // Advance data pointers and continue with next segment
         rx_window[vr_ur].buf->msg += len;
         rx_window[vr_ur].buf->N_bytes -= len;