diff --git a/bacnet-stack/ports/at91sam7s/dlmstp.c b/bacnet-stack/ports/at91sam7s/dlmstp.c
index 2b3d5a70..0cd79461 100644
--- a/bacnet-stack/ports/at91sam7s/dlmstp.c
+++ b/bacnet-stack/ports/at91sam7s/dlmstp.c
@@ -1122,6 +1122,8 @@ static bool MSTP_Master_Node_FSM(
                 Master_State = MSTP_MASTER_STATE_IDLE;
                 /* clear our flag we were holding for comparison */
                 MSTP_Flag.ReceivedValidFrame = false;
+                /* clear the queue */
+                (void) Ringbuf_Pop(&PDU_Queue, NULL);
             } else if ((Timer_Silence() > Treply_delay) || (pkt != NULL)) {
                 /* DeferredReply */
                 /* If no reply will be available from the higher layers */
diff --git a/bacnet-stack/ports/stm32f10x/dlmstp.c b/bacnet-stack/ports/stm32f10x/dlmstp.c
index a8811273..8b212ec4 100644
--- a/bacnet-stack/ports/stm32f10x/dlmstp.c
+++ b/bacnet-stack/ports/stm32f10x/dlmstp.c
@@ -1236,6 +1236,8 @@ static bool MSTP_Master_Node_FSM(
                 Master_State = MSTP_MASTER_STATE_IDLE;
                 /* clear our flag we were holding for comparison */
                 MSTP_Flag.ReceivedValidFrame = false;
+                /* clear the queue */
+                (void) Ringbuf_Pop(&PDU_Queue, NULL);
             } else if (rs485_silence_elapsed(Treply_delay) || (pkt != NULL)) {
                 /* DeferredReply */
                 /* If no reply will be available from the higher layers */