diff --git a/bootloader.c b/bootloader.c
index 83a9618..e7abd32 100644
--- a/bootloader.c
+++ b/bootloader.c
@@ -77,7 +77,7 @@ void main(void)
 	 * if the SP is not in this range (e.g. flash has been erased) there is no valid application
 	 * the second entry in the vector table is the reset address, corresponding to the application start
 	 */
-	volatile uint32_t* application = &__application_beginning; // get the value of the application address symbol (use a register instead on the stack since the stack pointer will be changed)
+	volatile uint32_t* application = (uint32_t*)&__application_beginning; // get the value of the application address symbol (use a register instead on the stack since the stack pointer will be changed)
 	if (!dfu_force && (((*application)&0xFFFE0000)==0x20000000)) { // application at address seems valid
 		SCB_VTOR = (volatile uint32_t)(application); // set vector table to application vector table (store at the beginning of the application)
 		__asm__ volatile ("MSR msp,%0" : :"r"(*application)); // set stack pointer to address provided in the beginning of the application (loaded into a register first)
diff --git a/global.h b/global.h
index e7267ee..e3e2817 100644
--- a/global.h
+++ b/global.h
@@ -20,7 +20,7 @@
 #pragma once
 
 /** enable debugging functionalities */
-#define DEBUG false
+#define DEBUG true
 
 /** get the length of an array */
 #define LENGTH(x) (sizeof(x) / sizeof((x)[0]))
@@ -422,11 +422,15 @@
 /** symbol for beginning of the application
  *  @note this symbol will be provided by the linker script
  */
-extern uint32_t __application_beginning;
+extern char __application_beginning;
 /** symbol for end of the application
  *  @note this symbol will be provided by the linker script
  */
-extern uint32_t __application_end;
+extern char __application_end;
+/** symbol for end of flash
+ *  @note this symbol will be provided by the linker script
+ */
+extern char __flash_end;
 /** flag set when board user button has been pressed/released */
 extern volatile bool button_flag;
 /** flag set when user input is available */
diff --git a/lib/flash_internal.c b/lib/flash_internal.c
index 540ba10..e55fed6 100644
--- a/lib/flash_internal.c
+++ b/lib/flash_internal.c
@@ -15,7 +15,7 @@
 /** library to read/write internal flash (code)
  *  @file flash_internal.c
  *  @author King Kévin <kingkevin@cuvoodoo.info>
- *  @date 2016
+ *  @date 2016-2018
  *  @note peripherals used: none
  */
 /* standard libraries */
@@ -30,20 +30,37 @@
 #include "flash_internal.h" // flash storage library API
 #include "global.h" // global definitions
 
+/** verify if the data is in the internal flash area
+ *  @param[in] address start address of the data to read
+ *  @param[in] size how much data to read or write, in bytes
+ *  @return if the data is in the internal flash area
+ */
+static bool flash_internal_range(uint32_t address, size_t size) {
+	if (address>(UINT32_MAX-size)) { // on integer overflow will occur
+		return false;
+	}
+	if (address<FLASH_BASE) { // start address is before the start of the internal flash
+		return false;
+	}
+	if ((uint32_t)&__flash_end>=FLASH_BASE) { // check if the end for the internal flash is enforce by the linker script
+		if ((address+size)>(uint32_t)&__flash_end) { // end address is after the end of the enforced internal flash
+			return false;
+		}
+	} else {
+		if ((address+size)>(FLASH_BASE+DESIG_FLASH_SIZE*1024)) { // end address is after the end of the advertised flash
+			return false;
+		}
+	}
+	return true;
+}
+
 bool flash_internal_read(uint32_t address, uint8_t *buffer, size_t size)
 {
 	// sanity checks
-	if (address<FLASH_BASE || address>(UINT32_MAX-size) || buffer==NULL || size==0) {
+	if (buffer==NULL || size==0) {
 		return false;
 	}
-
-	// verify if it's in the flash area
-#if defined(__flash_end)
-	if (address<FLASH_BASE || (address+size)>(uint32_t)&__flash_end)
-#else
-	if (address<FLASH_BASE || (address+size)>(FLASH_BASE+DESIG_FLASH_SIZE*1024))
-#endif
-	{
+	if (!flash_internal_range(address, size)) {
 		return false;
 	}
 
@@ -58,17 +75,19 @@ bool flash_internal_read(uint32_t address, uint8_t *buffer, size_t size)
 bool flash_internal_write(uint32_t address, uint8_t *buffer, size_t size)
 {
 	// sanity checks
-	if (address<FLASH_BASE || address>(UINT32_MAX-size) || buffer==NULL || size==0 || size%2) {
+	if (buffer==NULL || size==0 || size%2) {
+		return false;
+	}
+	if (!flash_internal_range(address, size)) {
 		return false;
 	}
 
 	// verify if it's in the flash area
-#if defined(__flash_end)
-	if (address<FLASH_BASE || (address+size)>(uint32_t)&__flash_end)
-#else
-	if (address<FLASH_BASE || (address+size)>(FLASH_BASE+DESIG_FLASH_SIZE*1024))
-#endif
-	{
+	if (address<FLASH_BASE) {
+		return false;
+	} else if ((uint32_t)&__flash_end>=FLASH_BASE && (address+size)>(uint32_t)&__flash_end) {
+		return false;
+	} else if ((uint32_t)&__flash_end<FLASH_BASE && (address+size)>(FLASH_BASE+DESIG_FLASH_SIZE*1024)) {
 		return false;
 	}
 
diff --git a/lib/usb_dfu.c b/lib/usb_dfu.c
index aa27a2d..a34f951 100644
--- a/lib/usb_dfu.c
+++ b/lib/usb_dfu.c
@@ -223,12 +223,12 @@ static int usb_dfu_control_request(usbd_device *usbd_dev, struct usb_setup_data
 					// we can only write half words
 					usb_dfu_status = DFU_STATUS_ERR_PROG;
 					usb_dfu_state = STATE_DFU_ERROR;
-#if defined(__application_end)
-				} else if (flash_pointer+*len>=(uint32_t)&__application_end) {
-#else
-				} else if (flash_pointer+*len>=(uint32_t)(FLASH_BASE+DESIG_FLASH_SIZE*1024)) {
-#endif
-					// application data is too large
+				} else if ((uint32_t)&__application_end>=FLASH_BASE && flash_pointer+*len>=(uint32_t)&__application_end) {
+					// application data is exceeding enforced flash size for application
+					usb_dfu_status = DFU_STATUS_ERR_ADDRESS;
+					usb_dfu_state = STATE_DFU_ERROR;
+				} else if ((uint32_t)&__application_end<FLASH_BASE && flash_pointer+*len>=(uint32_t)(FLASH_BASE+DESIG_FLASH_SIZE*1024)) {
+					// application data is exceeding advertised flash size
 					usb_dfu_status = DFU_STATUS_ERR_ADDRESS;
 					usb_dfu_state = STATE_DFU_ERROR;
 				} else {