diff --git a/cores/arduino/stm32/bootloader.h b/cores/arduino/stm32/bootloader.h
index 5e69157e12..93931dfb46 100644
--- a/cores/arduino/stm32/bootloader.h
+++ b/cores/arduino/stm32/bootloader.h
@@ -1,6 +1,8 @@
 #ifndef _BOOTLOADER_H_
 #define _BOOTLOADER_H_
 
+#include <stdint.h>
+
 /* Ensure DTR_TOGGLING_SEQ enabled */
 #if defined(BL_LEGACY_LEAF) || defined(BL_HID)
 #ifndef DTR_TOGGLING_SEQ
@@ -12,6 +14,11 @@
 extern "C" {
 #endif /* __cplusplus */
 
+#ifdef DTR_TOGGLING_SEQ
+/* DTR toggling sequence management */
+void dtr_togglingHook(uint8_t *buf, uint32_t *len);
+#endif
+
 #ifdef __cplusplus
 }
 #endif /* __cplusplus */
diff --git a/cores/arduino/stm32/usb/cdc/usbd_cdc_if.c b/cores/arduino/stm32/usb/cdc/usbd_cdc_if.c
index b4b1933a6a..c596b899f4 100644
--- a/cores/arduino/stm32/usb/cdc/usbd_cdc_if.c
+++ b/cores/arduino/stm32/usb/cdc/usbd_cdc_if.c
@@ -56,8 +56,6 @@ __IO bool receivePended = true;
 static uint32_t transmitStart = 0;
 
 #ifdef DTR_TOGGLING_SEQ
-/* DTR toggling sequence management */
-extern void dtr_togglingHook(uint8_t *buf, uint32_t *len);
 uint8_t dtr_toggling = 0;
 #endif