diff --git a/srsapps/ue/mac/src/mux.cc b/srsapps/ue/mac/src/mux.cc
index 8c291cfc3..e6935682e 100644
--- a/srsapps/ue/mac/src/mux.cc
+++ b/srsapps/ue/mac/src/mux.cc
@@ -124,8 +124,8 @@ void mux::set_priority(uint32_t lch_id, uint32_t set_priority, int set_PBR, uint
 
 void mux::pdu_release()
 {
-  pthread_mutex_unlock(&mutex);  
   pdu_buff.release();
+  pthread_mutex_unlock(&mutex);  
 }
 
 bool mux::pdu_move_to_msg3(uint32_t pdu_sz)
diff --git a/srsapps/ue/mac/src/ul_harq.cc b/srsapps/ue/mac/src/ul_harq.cc
index e71001b91..3d8bf69ad 100644
--- a/srsapps/ue/mac/src/ul_harq.cc
+++ b/srsapps/ue/mac/src/ul_harq.cc
@@ -125,6 +125,7 @@ void ul_harq_entity::run_tti(uint32_t tti, ul_sched_grant *grant, phy *phy_h)
           mux_unit->pdu_release();
           proc[pid].generate_new_tx(tti_tx, mac_pdu_buffer[pid], false, grant, phy_h->get_ul_buffer(tti_tx));          
         } else {
+          mux_unit->pdu_release();
           Warning("Uplink grant but no MAC PDU in Multiplex Unit buffer\n");
         }
       }