diff --git a/src/platforms/common/aux_serial.c b/src/platforms/common/aux_serial.c
index 8eaa3bd..2cd79bd 100644
--- a/src/platforms/common/aux_serial.c
+++ b/src/platforms/common/aux_serial.c
@@ -306,18 +306,11 @@ void aux_serial_update_receive_buffer_fullness(void)
 
 bool aux_serial_receive_has_data(void)
 {
-	return
-#ifdef ENABLE_DEBUG
-		usb_dbg_in != usb_dbg_out ||
-#endif
-		aux_serial_receive_write_index != aux_serial_receive_read_index;
+	return aux_serial_receive_write_index != aux_serial_receive_read_index;
 }
 
 void aux_serial_drain_receive_buffer(void)
 {
-#ifdef ENABLE_DEBUG
-	usb_dbg_out = usb_dbg_in;
-#endif
 	aux_serial_receive_read_index = aux_serial_receive_write_index;
 	/* Turn off LED */
 	usbuart_set_led_state(RX_LED_ACT, false);
diff --git a/src/platforms/common/usb_serial.c b/src/platforms/common/usb_serial.c
index 429c4a1..53c7c07 100644
--- a/src/platforms/common/usb_serial.c
+++ b/src/platforms/common/usb_serial.c
@@ -74,6 +74,13 @@ static bool aux_serial_receive_complete = true;
  * https://github.com/mirror/newlib-cygwin/blob/master/newlib/libc/sys/arm/syscalls.c#L115
  */
 void initialise_monitor_handles(void);
+
+/* Debug Fifo buffer with space for copy fn overrun */
+char usb_dbg_buf[AUX_UART_BUFFER_SIZE];
+/* Debug Fifo in pointer */
+uint8_t usb_dbg_in;
+/* Debug Fifo out pointer */
+uint8_t usb_dbg_out;
 #endif
 
 static enum usbd_request_return_codes gdb_uart_control_request(usbd_device *dev, struct usb_setup_data *req,
@@ -215,6 +222,13 @@ uint32_t debug_serial_fifo_send(const char *const fifo, const uint32_t fifo_begi
 	return fifo_begin;
 }
 
+#ifdef ENABLE_DEBUG
+static bool debug_serial_fifo_has_data(void)
+{
+	return usb_dbg_in != usb_dbg_out;
+}
+#endif
+
 /*
  * Runs deferred processing for AUX serial RX, draining RX FIFO by sending
  * characters to host PC via the debug serial interface.
@@ -226,7 +240,14 @@ static void debug_uart_send_aux_serial_data(void)
 
 	/* Forcibly empty fifo if no USB endpoint.
 	 * If fifo empty, nothing further to do. */
-	if (usb_get_config() != 1 || !aux_serial_receive_has_data()) {
+	if (usb_get_config() != 1 || (!aux_serial_receive_has_data()
+#ifdef ENABLE_DEBUG
+									 && !debug_serial_fifo_has_data())
+#endif
+	) {
+#ifdef ENABLE_DEBUG
+		usb_dbg_out = usb_dbg_in;
+#endif
 		aux_serial_drain_receive_buffer();
 		aux_serial_receive_complete = true;
 	} else {
diff --git a/src/platforms/common/usbuart.h b/src/platforms/common/usbuart.h
index 9c1d6a6..2885f6c 100644
--- a/src/platforms/common/usbuart.h
+++ b/src/platforms/common/usbuart.h
@@ -39,15 +39,6 @@ uint32_t debug_serial_fifo_send(const char *const fifo, const uint32_t fifo_begi
 
 #define USART_DMA_BUF_SIZE  (1U << USART_DMA_BUF_SHIFT)
 #define AUX_UART_BUFFER_SIZE (USART_DMA_BUF_SIZE)
-
-#ifdef ENABLE_DEBUG
-/* Debug Fifo buffer with space for copy fn overrun */
-extern char usb_dbg_buf[AUX_UART_BUFFER_SIZE];
-/* Debug Fifo in pointer */
-extern uint8_t usb_dbg_in;
-/* Debug Fifo out pointer */
-extern uint8_t usb_dbg_out;
-#endif
 #elif defined(LM4F)
 #define AUX_UART_BUFFER_SIZE 128
 #endif
diff --git a/src/platforms/stm32/usbuart.c b/src/platforms/stm32/usbuart.c
index d559f5a..7560ca7 100644
--- a/src/platforms/stm32/usbuart.c
+++ b/src/platforms/stm32/usbuart.c
@@ -31,12 +31,3 @@
 #include "usbuart.h"
 #include "usb.h"
 #include "aux_serial.h"
-
-#ifdef ENABLE_DEBUG
-/* Debug Fifo buffer with space for copy fn overrun */
-char usb_dbg_buf[AUX_UART_BUFFER_SIZE];
-/* Debug Fifo in pointer */
-uint8_t usb_dbg_in;
-/* Debug Fifo out pointer */
-uint8_t usb_dbg_out;
-#endif