diff --git a/include/os_io_usb.h b/include/os_io_usb.h
index d9b6d99c2..29def885e 100644
--- a/include/os_io_usb.h
+++ b/include/os_io_usb.h
@@ -50,6 +50,13 @@ io_usb_hid_receive_status_t io_usb_hid_receive(io_send_t      sndfct,
                                                unsigned short l,
                                                apdu_buffer_t *apdu_buffer);
 
+/**
+ * Read next HID transport packet, keep track of received APDU but discard content.
+ * Return true when an apdu is fully received (and discarded)
+ * To be called typically upon USB OUT event while an other apdu is being processed
+ */
+bool io_usb_hid_discard(unsigned char *buffer, unsigned short l);
+
 /**
  * Mark the last chunk transmitted as sent.
  * To be called typically upon USB IN ACK event
diff --git a/lib_blewbxx_impl/src/ledger_ble.c b/lib_blewbxx_impl/src/ledger_ble.c
index 94a2a71c8..7f1dbe363 100644
--- a/lib_blewbxx_impl/src/ledger_ble.c
+++ b/lib_blewbxx_impl/src/ledger_ble.c
@@ -452,10 +452,11 @@ static void init_mngr(uint16_t opcode, const uint8_t *buffer, uint16_t length)
             ledger_ble_data.hci_cmd_opcode = 0xfc0f;
             aci_hal_set_tx_power_level(1,  // High power (ignored)
 #ifdef TARGET_STAX
-                                       0x19);  // 0 dBm
-#else                                          // !TARGET_STAX
-                                       0x07);  // -14.1 dBm
-#endif                                         // !TARGET_STAX
+                                       0x19  // 0 dBm
+#else                                        // !TARGET_STAX
+                                       0x07  // -14.1 dBm
+#endif                                       // !TARGET_STAX
+            );
             break;
 
         case BLE_INIT_STEP_CONFIGURE_ADVERTISING:
@@ -510,7 +511,18 @@ static void hci_evt_cmd_complete(const uint8_t *buffer, uint16_t length)
         if (ledger_ble_data.transfer_mode_enable) {
             if ((ledger_protocol_data.rx_apdu_length)
                 && (ledger_protocol_data.rx_apdu_status == APDU_STATUS_COMPLETE)) {
-                copy_apdu_to_app(false);
+                if (G_io_app.apdu_state == APDU_IDLE) {
+                    copy_apdu_to_app(false);
+                }
+                else {
+                    // Discard received APDU and respond with error
+                    ledger_protocol_data.rx_apdu_length = 0;
+                    ledger_protocol_data.rx_apdu_status = APDU_STATUS_WAITING;
+                    uint8_t resp[2];
+                    U2BE_ENCODE(resp, 0, SWO_IOL_STA_02);
+                    LEDGER_PROTOCOL_tx(resp, 2);
+                    notify_chunk();
+                }
             }
         }
         else {
@@ -521,7 +533,9 @@ static void hci_evt_cmd_complete(const uint8_t *buffer, uint16_t length)
             if (!ledger_protocol_data.tx_apdu_buffer) {
                 ledger_protocol_data.tx_chunk_length = 0;
                 G_io_app.ble_xfer_timeout            = 0;
-                G_io_app.apdu_state                  = APDU_IDLE;
+                if (G_io_app.apdu_state == APDU_BLE) {
+                    G_io_app.apdu_state = APDU_IDLE;
+                }
                 if ((!ledger_ble_data.connection_updated)
                     && (ledger_ble_data.connection.conn_interval > BLE_SLAVE_CONN_INTERVAL_MIN)) {
                     ledger_ble_data.connection_updated = 1;
@@ -872,7 +886,18 @@ static void attribute_modified(const uint8_t *buffer, uint16_t length)
                     LOG_BLE("Transfer failed 0x%04x\n", U2BE(ledger_ble_data.resp, 0));
                     G_io_app.transfer_mode = 0;
                     check_transfer_mode(G_io_app.transfer_mode);
-                    copy_apdu_to_app(true);
+                    if (G_io_app.apdu_state == APDU_IDLE) {
+                        copy_apdu_to_app(true);
+                    }
+                    else {
+                        // Discard received APDU and respond with error
+                        ledger_protocol_data.rx_apdu_length = 0;
+                        ledger_protocol_data.rx_apdu_status = APDU_STATUS_WAITING;
+                        uint8_t resp[2];
+                        U2BE_ENCODE(resp, 0, SWO_IOL_STA_02);
+                        LEDGER_PROTOCOL_tx(resp, 2);
+                        notify_chunk();
+                    }
                 }
                 else if (ledger_ble_data.resp_length) {
                     LEDGER_PROTOCOL_tx(ledger_ble_data.resp, ledger_ble_data.resp_length);
@@ -881,13 +906,25 @@ static void attribute_modified(const uint8_t *buffer, uint16_t length)
                 }
             }
             else {
-                copy_apdu_to_app(true);
+                // Nominal case for apdu reception
+                if (G_io_app.apdu_state == APDU_IDLE) {
+                    copy_apdu_to_app(true);
+                }
+                else {
+                    // Discard received APDU and respond with error
+                    ledger_protocol_data.rx_apdu_length = 0;
+                    ledger_protocol_data.rx_apdu_status = APDU_STATUS_WAITING;
+                    uint8_t resp[2];
+                    U2BE_ENCODE(resp, 0, SWO_IOL_STA_02);
+                    LEDGER_PROTOCOL_tx(resp, 2);
+                    notify_chunk();
+                }
             }
         }
         else if (ledger_protocol_data.tx_chunk_length >= 2) {
+            // apdu not complete yet
             G_io_app.ble_xfer_timeout = 2000;
             notify_chunk();
-            G_io_app.apdu_state = APDU_BLE;
         }
     }
     else {
@@ -917,7 +954,18 @@ static void write_permit_request(const uint8_t *buffer, uint16_t length)
                             data_length,
                             &buffer[3]);
         if (ledger_protocol_data.rx_apdu_status == APDU_STATUS_COMPLETE) {
-            copy_apdu_to_app(true);
+            if (G_io_app.apdu_state == APDU_IDLE) {
+                copy_apdu_to_app(true);
+            }
+            else {
+                // Discard received APDU and respond with error
+                ledger_protocol_data.rx_apdu_length = 0;
+                ledger_protocol_data.rx_apdu_status = APDU_STATUS_WAITING;
+                uint8_t resp[2];
+                U2BE_ENCODE(resp, 0, SWO_IOL_STA_02);
+                LEDGER_PROTOCOL_tx(resp, 2);
+                notify_chunk();
+            }
         }
     }
     else {
@@ -1040,7 +1088,9 @@ void LEDGER_BLE_set_recv_buffer(uint8_t *buffer, uint16_t buffer_length)
 void LEDGER_BLE_send(const uint8_t *packet, uint16_t packet_length)
 {
     if ((ledger_ble_data.transfer_mode_enable != 0) && (packet_length == 2)) {
-        G_io_app.apdu_state         = APDU_IDLE;
+        if (G_io_app.apdu_state == APDU_BLE) {
+            G_io_app.apdu_state = APDU_IDLE;
+        }
         ledger_ble_data.resp_length = 2;
         ledger_ble_data.resp[0]     = packet[0];
         ledger_ble_data.resp[1]     = packet[1];
diff --git a/lib_standard_app/io.c b/lib_standard_app/io.c
index 90b8f4105..c56299643 100644
--- a/lib_standard_app/io.c
+++ b/lib_standard_app/io.c
@@ -63,9 +63,9 @@ WEAK uint8_t io_event(uint8_t channel)
 #endif  // HAVE_BAGL
             break;
         case SEPROXYHAL_TAG_STATUS_EVENT:
-            if (G_io_apdu_media == IO_APDU_MEDIA_USB_HID &&  //
-                !(U4BE(G_io_seproxyhal_spi_buffer, 3) &      //
-                  SEPROXYHAL_TAG_STATUS_EVENT_FLAG_USB_POWERED)) {
+            if (G_io_apdu_media == IO_APDU_MEDIA_USB_HID
+                && !(U4BE(G_io_seproxyhal_spi_buffer, 3)
+                     & SEPROXYHAL_TAG_STATUS_EVENT_FLAG_USB_POWERED)) {
                 THROW(EXCEPTION_IO_RESET);
             }
             __attribute__((fallthrough));
diff --git a/lib_stusb/STM32_USB_Device_Library/Class/CCID/src/usbd_ccid_if.c b/lib_stusb/STM32_USB_Device_Library/Class/CCID/src/usbd_ccid_if.c
index ef0302615..e2c9331ca 100644
--- a/lib_stusb/STM32_USB_Device_Library/Class/CCID/src/usbd_ccid_if.c
+++ b/lib_stusb/STM32_USB_Device_Library/Class/CCID/src/usbd_ccid_if.c
@@ -138,7 +138,9 @@ void CCID_BulkMessage_In (USBD_HandleTypeDef  *pdev,
         // not timeout compliant // USBD_LL_PrepareReceive(pdev, CCID_BULK_OUT_EP, CCID_BULK_EPOUT_SIZE);
 
         // mark transfer as completed
-        G_io_app.apdu_state = APDU_IDLE;
+        if (G_io_app.apdu_state == APDU_USB_CCID){
+          G_io_app.apdu_state = APDU_IDLE;
+        }
       }
 
       // if remaining length is < EPIN_SIZE: send packet and prepare to receive a new command
diff --git a/lib_stusb_impl/usbd_impl.c b/lib_stusb_impl/usbd_impl.c
index 7fdfac406..de07639f6 100644
--- a/lib_stusb_impl/usbd_impl.c
+++ b/lib_stusb_impl/usbd_impl.c
@@ -1036,7 +1036,7 @@ uint8_t USBD_HID_DataOut_impl(USBD_HandleTypeDef *pdev,
 
 #ifndef HAVE_USB_HIDKBD
             // avoid troubles when an apdu has not been replied yet
-            if (G_io_app.apdu_media == IO_APDU_MEDIA_NONE) {
+            if (G_io_app.apdu_state == APDU_IDLE) {
                 // add to the hid transport
                 switch (io_usb_hid_receive(io_usb_send_apdu_data,
                                            buffer,
@@ -1052,6 +1052,14 @@ uint8_t USBD_HID_DataOut_impl(USBD_HandleTypeDef *pdev,
                         break;
                 }
             }
+            else {
+                if (io_usb_hid_discard(buffer, io_seproxyhal_get_ep_rx_size(HID_EPOUT_ADDR))) {
+                    // Discarded new APDU, send error response
+                    unsigned char resp_apdu[2] = {};
+                    U2BE_ENCODE(resp_apdu, 0, SWO_IOL_STA_02);
+                    io_usb_hid_send(io_usb_send_apdu_data, 2, resp_apdu);
+                }
+            }
 #endif  // HAVE_USB_HIDKBD
             break;
     }
@@ -1116,7 +1124,7 @@ uint8_t USBD_WEBUSB_DataOut(USBD_HandleTypeDef *pdev,
             USBD_LL_PrepareReceive(pdev, WEBUSB_EPOUT_ADDR, WEBUSB_EPOUT_SIZE);
 
             // avoid troubles when an apdu has not been replied yet
-            if (G_io_app.apdu_media == IO_APDU_MEDIA_NONE) {
+            if (G_io_app.apdu_state == APDU_IDLE) {
                 // add to the hid transport
                 switch (io_usb_hid_receive(io_usb_send_apdu_data_ep0x83,
                                            buffer,
@@ -1132,6 +1140,14 @@ uint8_t USBD_WEBUSB_DataOut(USBD_HandleTypeDef *pdev,
                         break;
                 }
             }
+            else {
+                if (io_usb_hid_discard(buffer, io_seproxyhal_get_ep_rx_size(WEBUSB_EPOUT_ADDR))) {
+                    // Discarded new APDU, send error response
+                    unsigned char resp_apdu[2] = {};
+                    U2BE_ENCODE(resp_apdu, 0, SWO_IOL_STA_02);
+                    io_usb_hid_send(io_usb_send_apdu_data_ep0x83, 2, resp_apdu);
+                }
+            }
             break;
     }
 
diff --git a/lib_u2f/src/u2f_transport.c b/lib_u2f/src/u2f_transport.c
index 4334fdd5c..7a71cfbd6 100644
--- a/lib_u2f/src/u2f_transport.c
+++ b/lib_u2f/src/u2f_transport.c
@@ -154,7 +154,9 @@ void u2f_transport_sent(u2f_service_t *service, u2f_transport_media_t media)
         u2f_transport_reset(service);
         // we sent the whole response (even if we haven't yet received the ack for the last sent usb
         // in packet)
-        G_io_app.apdu_state = APDU_IDLE;
+        if (G_io_app.apdu_state == APDU_U2F) {
+            G_io_app.apdu_state = APDU_IDLE;
+        }
     }
 }
 
diff --git a/src/os_io_seproxyhal.c b/src/os_io_seproxyhal.c
index d89af470a..cd3d96659 100644
--- a/src/os_io_seproxyhal.c
+++ b/src/os_io_seproxyhal.c
@@ -241,19 +241,37 @@ void io_seproxyhal_handle_capdu_event(void)
         // copy apdu to apdu buffer
         memcpy(G_io_apdu_buffer, G_io_seproxyhal_spi_buffer + 3, G_io_app.apdu_length);
     }
+    else {
+        // Refuse APDU, send error reply
+        G_io_seproxyhal_spi_buffer[0] = SEPROXYHAL_TAG_RAPDU;
+        G_io_seproxyhal_spi_buffer[1] = 0;
+        G_io_seproxyhal_spi_buffer[2] = 2;
+        U2BE_ENCODE(G_io_seproxyhal_spi_buffer, 3, SWO_IOL_STA_02);
+        io_seproxyhal_spi_send(G_io_seproxyhal_spi_buffer, 5);
+    }
 }
 
 #ifdef HAVE_NFC
 void io_seproxyhal_handle_nfc_recv_event(void)
 {
-    size_t max  = MIN(sizeof(G_io_apdu_buffer), sizeof(G_io_seproxyhal_spi_buffer) - 3);
-    size_t size = U2BE(G_io_seproxyhal_spi_buffer, 1);
+    if (G_io_app.apdu_state == APDU_IDLE) {
+        size_t max  = MIN(sizeof(G_io_apdu_buffer), sizeof(G_io_seproxyhal_spi_buffer) - 3);
+        size_t size = U2BE(G_io_seproxyhal_spi_buffer, 1);
 
-    G_io_app.apdu_media  = IO_APDU_MEDIA_NFC;
-    G_io_app.apdu_state  = APDU_NFC;
-    G_io_app.apdu_length = MIN(size, max);
+        G_io_app.apdu_media  = IO_APDU_MEDIA_NFC;
+        G_io_app.apdu_state  = APDU_NFC;
+        G_io_app.apdu_length = MIN(size, max);
 
-    memcpy(G_io_apdu_buffer, &G_io_seproxyhal_spi_buffer[3], G_io_app.apdu_length);
+        memcpy(G_io_apdu_buffer, &G_io_seproxyhal_spi_buffer[3], G_io_app.apdu_length);
+    }
+    else {
+        // Refuse APDU, send error reply
+        G_io_seproxyhal_spi_buffer[0] = SEPROXYHAL_TAG_NFC_RAPDU;
+        G_io_seproxyhal_spi_buffer[1] = 0;
+        G_io_seproxyhal_spi_buffer[2] = 2;
+        U2BE_ENCODE(G_io_seproxyhal_spi_buffer, 3, SWO_IOL_STA_02);
+        io_seproxyhal_spi_send(G_io_seproxyhal_spi_buffer, 5);
+    }
 }
 #endif
 unsigned int io_seproxyhal_handle_event(void)
@@ -1364,7 +1382,7 @@ unsigned short io_exchange(unsigned char channel, unsigned short tx_len)
                             io_seproxyhal_spi_send(G_io_seproxyhal_spi_buffer, 3);
                             io_seproxyhal_spi_send(G_io_apdu_buffer, tx_len);
 
-                            // isngle packet reply, mark immediate idle
+                            // single packet reply, mark immediate idle
                             G_io_app.apdu_state = APDU_IDLE;
                             G_io_app.apdu_media = IO_APDU_MEDIA_NONE;
                             goto break_send;
@@ -1381,8 +1399,9 @@ unsigned short io_exchange(unsigned char channel, unsigned short tx_len)
                             io_seproxyhal_spi_send(G_io_seproxyhal_spi_buffer, 3);
                             io_seproxyhal_spi_send(G_io_apdu_buffer, tx_len);
 
-                            // isngle packet reply, mark immediate idle
+                            // single packet reply, mark immediate idle
                             G_io_app.apdu_state = APDU_IDLE;
+                            G_io_app.apdu_media = IO_APDU_MEDIA_NONE;
                             // finished, no chunking
                             goto break_send;
 
diff --git a/src/os_io_usb.c b/src/os_io_usb.c
index 5af0ee509..e65ea3d61 100644
--- a/src/os_io_usb.c
+++ b/src/os_io_usb.c
@@ -238,6 +238,45 @@ io_usb_hid_receive_status_t io_usb_hid_receive(io_send_t      sndfct,
     return IO_USB_APDU_RESET;
 }
 
+bool io_usb_hid_discard(unsigned char *buffer, unsigned short l)
+{
+    static unsigned int seq_number       = 0;
+    static unsigned int remaining_length = 0;
+
+    if (buffer[2] != 0x05) {
+        return false;
+    }
+
+    // ensure sequence idx is 0 for the first chunk
+    if ((unsigned int) U2BE(buffer, 3) != (unsigned int) seq_number) {
+        // ignore packet
+        seq_number       = 0;
+        remaining_length = 0;
+        return false;
+    }
+
+    // cid, tag, seq
+    l -= 2 + 1 + 2;
+
+    if (seq_number == 0) {
+        // total apdu size to receive
+        remaining_length = U2BE(buffer, 5);
+        l -= 2;
+    }
+    if (l > remaining_length) {
+        l = remaining_length;
+    }
+    remaining_length -= l;
+    seq_number++;
+
+    // Full apdu received, reset sequence number for next time
+    if (remaining_length == 0) {
+        seq_number = 0;
+        return true;
+    }
+    return false;
+}
+
 void io_usb_hid_init(void)
 {
     G_io_usb_hid_sequence_number  = 0;
@@ -293,7 +332,9 @@ void io_usb_hid_sent(io_send_t sndfct)
         io_usb_hid_init();
 
         // we sent the whole response
-        G_io_app.apdu_state = APDU_IDLE;
+        if (G_io_app.apdu_state == APDU_USB_HID || G_io_app.apdu_state == APDU_USB_WEBUSB) {
+            G_io_app.apdu_state = APDU_IDLE;
+        }
     }
 }