diff --git a/radio/src/gui/Taranis/view_statistics.cpp b/radio/src/gui/Taranis/view_statistics.cpp
index 015bba569..001c32e81 100755
--- a/radio/src/gui/Taranis/view_statistics.cpp
+++ b/radio/src/gui/Taranis/view_statistics.cpp
@@ -104,7 +104,7 @@ void menuStatisticsView(uint8_t event)
 #if defined(USB_SERIAL)
   extern uint16_t usbWraps;
   extern uint16_t charsWritten;
-  extern "C" uint32_t APP_Rx_ptr_in;
+  extern "C" volatile uint32_t APP_Rx_ptr_in;
 #endif
 
 void menuStatisticsDebug(uint8_t event)
diff --git a/radio/src/targets/taranis/usbd_cdc.cpp b/radio/src/targets/taranis/usbd_cdc.cpp
index ef4543eec..7cb2d061a 100644
--- a/radio/src/targets/taranis/usbd_cdc.cpp
+++ b/radio/src/targets/taranis/usbd_cdc.cpp
@@ -47,10 +47,10 @@ extern "C" {
 extern uint8_t  APP_Rx_Buffer []; /* Write CDC received data in this buffer.
                                      These data will be sent over USB IN endpoint
                                      in the CDC core functions. */
-extern uint32_t APP_Rx_ptr_in;    /* Increment this pointer or roll it back to
+extern volatile uint32_t APP_Rx_ptr_in;    /* Increment this pointer or roll it back to
                                      start address when writing received data
                                      in the buffer APP_Rx_Buffer. */
-extern uint32_t APP_Rx_ptr_out;
+extern volatile uint32_t APP_Rx_ptr_out;
 
 /* Private function prototypes -----------------------------------------------*/
 static uint16_t VCP_Init     (void);
@@ -162,13 +162,13 @@ void usbSerialPutc(uint8_t c)
 {
   if (!cdcConnected) return;
 
-  uint32_t APP_Rx_length;
+  uint32_t txDataLen;
   do {
-    APP_Rx_length = APP_RX_DATA_SIZE + APP_Rx_ptr_in - APP_Rx_ptr_out;
-    if (APP_Rx_length >= APP_RX_DATA_SIZE) {
-      APP_Rx_length -= APP_RX_DATA_SIZE;
+    txDataLen = APP_RX_DATA_SIZE + APP_Rx_ptr_in - APP_Rx_ptr_out;
+    if (txDataLen >= APP_RX_DATA_SIZE) {
+      txDataLen -= APP_RX_DATA_SIZE;
     }
-  } while (APP_Rx_length == APP_RX_DATA_SIZE-1);
+  } while (txDataLen >= (APP_RX_DATA_SIZE - CDC_DATA_MAX_PACKET_SIZE));
 
   APP_Rx_Buffer[APP_Rx_ptr_in] = c;
   ++charsWritten;
diff --git a/radio/src/thirdparty/STM32_USB-Host-Device_Lib_V2.1.0/Libraries/STM32_USB_Device_Library/Class/cdc/src/usbd_cdc_core.c b/radio/src/thirdparty/STM32_USB-Host-Device_Lib_V2.1.0/Libraries/STM32_USB_Device_Library/Class/cdc/src/usbd_cdc_core.c
index c0ed18c58..3856f778d 100644
--- a/radio/src/thirdparty/STM32_USB-Host-Device_Lib_V2.1.0/Libraries/STM32_USB_Device_Library/Class/cdc/src/usbd_cdc_core.c
+++ b/radio/src/thirdparty/STM32_USB-Host-Device_Lib_V2.1.0/Libraries/STM32_USB_Device_Library/Class/cdc/src/usbd_cdc_core.c
@@ -179,8 +179,8 @@ __ALIGN_BEGIN uint8_t APP_Rx_Buffer   [APP_RX_DATA_SIZE] __ALIGN_END ;
 #endif /* USB_OTG_HS_INTERNAL_DMA_ENABLED */
 __ALIGN_BEGIN uint8_t CmdBuff[CDC_CMD_PACKET_SZE] __ALIGN_END ;
 
-uint32_t APP_Rx_ptr_in  = 0;
-uint32_t APP_Rx_ptr_out = 0;
+volatile uint32_t APP_Rx_ptr_in  = 0;
+volatile uint32_t APP_Rx_ptr_out = 0;
 uint32_t APP_Rx_length  = 0;
 
 uint8_t  USB_Tx_State = 0;