diff --git a/lib/include/srsran/rlc/rlc_am_base.h b/lib/include/srsran/rlc/rlc_am_base.h
index 27f1f3555..c5f8786f6 100644
--- a/lib/include/srsran/rlc/rlc_am_base.h
+++ b/lib/include/srsran/rlc/rlc_am_base.h
@@ -134,7 +134,6 @@ public:
     virtual void     get_buffer_state(uint32_t& tx_queue, uint32_t& prio_tx_queue) = 0;
     virtual void     reestablish()                                                 = 0;
     virtual void     empty_queue()                                                 = 0;
-    virtual void     discard_sdu(uint32_t pdcp_sn)                                 = 0;
     virtual bool     sdu_queue_is_full()                                           = 0;
     virtual bool     has_data()                                                    = 0;
     virtual void     stop()                                                        = 0;
@@ -142,6 +141,7 @@ public:
     void set_bsr_callback(bsr_callback_t callback);
 
     int              write_sdu(unique_byte_buffer_t sdu);
+    virtual void     discard_sdu(uint32_t pdcp_sn);
     virtual uint32_t read_pdu(uint8_t* payload, uint32_t nof_bytes) = 0;
 
     bool                  tx_enabled = false;
diff --git a/lib/include/srsran/rlc/rlc_am_lte.h b/lib/include/srsran/rlc/rlc_am_lte.h
index 4a1cf9c4b..90031dae8 100644
--- a/lib/include/srsran/rlc/rlc_am_lte.h
+++ b/lib/include/srsran/rlc/rlc_am_lte.h
@@ -59,7 +59,6 @@ public:
   void stop();
 
   uint32_t read_pdu(uint8_t* payload, uint32_t nof_bytes);
-  void     discard_sdu(uint32_t discard_sn);
   bool     sdu_queue_is_full();
 
   bool     has_data();
diff --git a/lib/include/srsran/rlc/rlc_am_nr.h b/lib/include/srsran/rlc/rlc_am_nr.h
index e0d44bd55..b7ec41552 100644
--- a/lib/include/srsran/rlc/rlc_am_nr.h
+++ b/lib/include/srsran/rlc/rlc_am_nr.h
@@ -97,7 +97,6 @@ public:
   uint32_t read_pdu(uint8_t* payload, uint32_t nof_bytes) final;
   void     handle_control_pdu(uint8_t* payload, uint32_t nof_bytes) final;
 
-  void discard_sdu(uint32_t discard_sn) final;
   bool sdu_queue_is_full() final;
   void reestablish() final;
 
diff --git a/lib/include/srsran/rlc/rlc_um_lte.h b/lib/include/srsran/rlc/rlc_um_lte.h
index 8da49c646..48bf889ca 100644
--- a/lib/include/srsran/rlc/rlc_um_lte.h
+++ b/lib/include/srsran/rlc/rlc_um_lte.h
@@ -49,6 +49,7 @@ private:
 
     bool     configure(const rlc_config_t& cfg, std::string rb_name);
     uint32_t build_data_pdu(unique_byte_buffer_t pdu, uint8_t* payload, uint32_t nof_bytes);
+    void     discard_sdu(uint32_t discard_sn);
     uint32_t get_buffer_state();
     bool     sdu_queue_is_full();
 
diff --git a/lib/include/srsran/rlc/rlc_um_nr.h b/lib/include/srsran/rlc/rlc_um_nr.h
index 7e5b860ba..f74d59964 100644
--- a/lib/include/srsran/rlc/rlc_um_nr.h
+++ b/lib/include/srsran/rlc/rlc_um_nr.h
@@ -53,6 +53,7 @@ private:
 
     bool     configure(const rlc_config_t& cfg, std::string rb_name);
     uint32_t build_data_pdu(unique_byte_buffer_t pdu, uint8_t* payload, uint32_t nof_bytes);
+    void     discard_sdu(uint32_t discard_sn);
     uint32_t get_buffer_state();
 
   private:
diff --git a/lib/src/rlc/rlc_am_base.cc b/lib/src/rlc/rlc_am_base.cc
index c2f7978b0..605b1f494 100644
--- a/lib/src/rlc/rlc_am_base.cc
+++ b/lib/src/rlc/rlc_am_base.cc
@@ -235,6 +235,25 @@ int rlc_am::rlc_am_base_tx::write_sdu(unique_byte_buffer_t sdu)
   return SRSRAN_SUCCESS;
 }
 
+void rlc_am::rlc_am_base_tx::discard_sdu(uint32_t discard_sn)
+{
+  std::lock_guard<std::mutex> lock(mutex);
+
+  if (!tx_enabled) {
+    return;
+  }
+  bool discarded = tx_sdu_queue.apply_first([&discard_sn, this](unique_byte_buffer_t& sdu) {
+    if (sdu != nullptr && sdu->md.pdcp_sn == discard_sn) {
+      tx_sdu_queue.queue.pop_func(sdu);
+      sdu = nullptr;
+    }
+    return false;
+  });
+
+  // Discard fails when the PDCP PDU is already in Tx window.
+  RlcInfo("%s PDU with PDCP_SN=%d", discarded ? "Discarding" : "Couldn't discard", discard_sn);
+}
+
 void rlc_am::rlc_am_base_tx::set_bsr_callback(bsr_callback_t callback)
 {
   bsr_callback = callback;
diff --git a/lib/src/rlc/rlc_am_lte.cc b/lib/src/rlc/rlc_am_lte.cc
index 1b3218c84..097acc769 100644
--- a/lib/src/rlc/rlc_am_lte.cc
+++ b/lib/src/rlc/rlc_am_lte.cc
@@ -268,24 +268,6 @@ void rlc_am_lte_tx::get_buffer_state_nolock(uint32_t& n_bytes_newtx, uint32_t& n
   }
 }
 
-void rlc_am_lte_tx::discard_sdu(uint32_t discard_sn)
-{
-  if (!tx_enabled) {
-    return;
-  }
-
-  bool discarded = tx_sdu_queue.apply_first([&discard_sn, this](unique_byte_buffer_t& sdu) {
-    if (sdu != nullptr && sdu->md.pdcp_sn == discard_sn) {
-      tx_sdu_queue.queue.pop_func(sdu);
-      sdu = nullptr;
-    }
-    return false;
-  });
-
-  // Discard fails when the PDCP PDU is already in Tx window.
-  RlcInfo("%s PDU with PDCP_SN=%d", discarded ? "Discarding" : "Couldn't discard", discard_sn);
-}
-
 bool rlc_am_lte_tx::sdu_queue_is_full()
 {
   return tx_sdu_queue.is_full();
diff --git a/lib/src/rlc/rlc_am_nr.cc b/lib/src/rlc/rlc_am_nr.cc
index 13e25ef3a..bdb1c2792 100644
--- a/lib/src/rlc/rlc_am_nr.cc
+++ b/lib/src/rlc/rlc_am_nr.cc
@@ -856,8 +856,6 @@ void rlc_am_nr_tx::reestablish()
   stop();
 }
 
-void rlc_am_nr_tx::discard_sdu(uint32_t discard_sn) {}
-
 bool rlc_am_nr_tx::sdu_queue_is_full()
 {
   return false;
diff --git a/lib/src/rlc/rlc_um_base.cc b/lib/src/rlc/rlc_um_base.cc
index b39e7d34c..0c8604004 100644
--- a/lib/src/rlc/rlc_um_base.cc
+++ b/lib/src/rlc/rlc_um_base.cc
@@ -298,7 +298,18 @@ int rlc_um_base::rlc_um_base_tx::try_write_sdu(unique_byte_buffer_t sdu)
 
 void rlc_um_base::rlc_um_base_tx::discard_sdu(uint32_t discard_sn)
 {
-  RlcWarning("RLC UM: Discard SDU not implemented yet.");
+  std::lock_guard<std::mutex> lock(mutex);
+
+  bool discarded = tx_sdu_queue.apply_first([&discard_sn, this](unique_byte_buffer_t& sdu) {
+    if (sdu != nullptr && sdu->md.pdcp_sn == discard_sn) {
+      tx_sdu_queue.queue.pop_func(sdu);
+      sdu = nullptr;
+    }
+    return false;
+  });
+
+  // Discard fails when the PDCP PDU is already in Tx window.
+  RlcInfo("%s PDU with PDCP_SN=%d", discarded ? "Discarding" : "Couldn't discard", discard_sn);
 }
 
 bool rlc_um_base::rlc_um_base_tx::sdu_queue_is_full()