diff --git a/lib/include/srsran/rlc/rlc_am_nr.h b/lib/include/srsran/rlc/rlc_am_nr.h
index 0a70639fb..42bf858d7 100644
--- a/lib/include/srsran/rlc/rlc_am_nr.h
+++ b/lib/include/srsran/rlc/rlc_am_nr.h
@@ -131,6 +131,7 @@ public:
 
   // Window helpers
   bool inside_tx_window(uint32_t sn) const;
+  bool valid_ack_sn(uint32_t sn) const;
 
 private:
   rlc_am*       parent = nullptr;
@@ -240,6 +241,7 @@ public:
   int  handle_full_data_sdu(const rlc_am_nr_pdu_header_t& header, const uint8_t* payload, uint32_t nof_bytes);
   int  handle_segment_data_sdu(const rlc_am_nr_pdu_header_t& header, const uint8_t* payload, uint32_t nof_bytes);
   bool inside_rx_window(uint32_t sn);
+  bool valid_ack_sn(uint32_t sn);
   void write_to_upper_layers(uint32_t lcid, unique_byte_buffer_t sdu);
   void insert_received_segment(rlc_amd_rx_pdu_nr segment, rlc_amd_rx_sdu_nr_t::segment_list_t& segment_list) const;
   /**
diff --git a/lib/src/rlc/rlc_am_nr.cc b/lib/src/rlc/rlc_am_nr.cc
index 0acdbe273..5cf175917 100644
--- a/lib/src/rlc/rlc_am_nr.cc
+++ b/lib/src/rlc/rlc_am_nr.cc
@@ -1309,6 +1309,12 @@ bool rlc_am_nr_tx::inside_tx_window(uint32_t sn) const
   return tx_mod_base_nr(sn) < tx_window_size();
 }
 
+bool rlc_am_nr_tx::valid_ack_sn(uint32_t sn)
+{
+  // Tx_Next_Ack < SN <= TX_Next + AM_Window_Size
+  return (0 < tx_mod_base_nr(sn)) && (tx_mod_base_nr(sn) <= tx_window_size());
+}
+
 /*
  * Debug Helpers
  */
@@ -1844,11 +1850,11 @@ void rlc_am_nr_rx::timer_expired(uint32_t timeout_id)
       }
     }
     st.rx_highest_status = sn_upd;
-    if (not inside_rx_window(st.rx_highest_status)) {
+    if (not valid_ack_sn(st.rx_highest_status)) {
       RlcError("Rx_Highest_Status not inside RX window");
       debug_state();
     }
-    srsran_assert(inside_rx_window(st.rx_highest_status), "Error: rx_highest_status assigned outside rx window");
+    srsran_assert(valid_ack_sn(st.rx_highest_status), "Error: rx_highest_status assigned outside rx window");
 
     bool restart_reassembly_timer = false;
     if (rx_mod_base_nr(st.rx_next_highest) > rx_mod_base_nr(st.rx_highest_status + 1)) {
@@ -1943,6 +1949,12 @@ bool rlc_am_nr_rx::inside_rx_window(uint32_t sn)
   return rx_mod_base_nr(sn) < rx_window_size();
 }
 
+bool rlc_am_nr_rx::valid_ack_sn(uint32_t sn)
+{
+  // RX_Next < SN <= RX_Next + AM_Window_Size
+  return (0 < rx_mod_base_nr(sn)) && (rx_mod_base_nr(sn) <= rx_window_size());
+}
+
 /*
  * Debug Helpers
  */