diff --git a/ion/src/device/usb/Makefile b/ion/src/device/usb/Makefile
index a2d840eef..6a859fcc9 100644
--- a/ion/src/device/usb/Makefile
+++ b/ion/src/device/usb/Makefile
@@ -50,6 +50,7 @@ dfu_objs += ion/src/device/device.o
 dfu_objs += ion/src/device/usb.o
 dfu_objs += ion/src/device/base64.o
 dfu_objs += ion/src/device/flash.o
+dfu_objs += ion/src/device/external_flash.o
 dfu_objs += ion/src/device/timing.o
 
 ion/src/device/usb/dfu.elf: LDSCRIPT = ion/src/device/usb/dfu.ld
diff --git a/ion/src/device/usb/calculator.h b/ion/src/device/usb/calculator.h
index d3383e419..81b8c9b2a 100644
--- a/ion/src/device/usb/calculator.h
+++ b/ion/src/device/usb/calculator.h
@@ -93,7 +93,7 @@ public:
     m_manufacturerStringDescriptor("NumWorks"),
     m_productStringDescriptor("NumWorks Calculator"),
     m_serialNumberStringDescriptor(serialNumber),
-    m_interfaceStringDescriptor("@Flash/0x08000000/04*016Kg,01*064Kg,07*128Kg"),
+    m_interfaceStringDescriptor("@Flash/0x08000000/04*016Kg,01*064Kg,07*128Kg/0x90000000/64*064Kg,64*064Kg"),
     //m_interfaceStringDescriptor("@SRAM/0x20000000/01*256Ke"),
     /* Switch to this descriptor to use dfu-util to write in the SRAM.
      * FIXME Should be an alternate Interface. */
diff --git a/ion/src/device/usb/dfu_interface.cpp b/ion/src/device/usb/dfu_interface.cpp
index 029cce703..8b30e7ea2 100644
--- a/ion/src/device/usb/dfu_interface.cpp
+++ b/ion/src/device/usb/dfu_interface.cpp
@@ -1,6 +1,7 @@
 #include "dfu_interface.h"
 #include <string.h>
 #include <ion/src/device/flash.h>
+#include <ion/src/device/external_flash.h>
 
 namespace Ion {
 namespace USB {
@@ -173,7 +174,7 @@ void DFUInterface::eraseCommand(uint8_t * transferBuffer, uint16_t transferBuffe
 
   if (transferBufferLength == 1) {
     // Mass erase
-    m_erasePage = Flash::Device::NumberOfSectors;
+    m_erasePage = Flash::Device::NumberOfSectors + ExternalFlash::Device::NumberOfSectors;
     return;
   }
 
@@ -185,9 +186,11 @@ void DFUInterface::eraseCommand(uint8_t * transferBuffer, uint16_t transferBuffe
     + (transferBuffer[3] << 16)
     + (transferBuffer[4] << 24);
 
-  m_erasePage = Flash::Device::SectorAtAddress(eraseAddress);
-
-  if (m_erasePage < 0) {
+  if (eraseAddress >= k_flashStartAddress && eraseAddress <= k_flashEndAddress) {
+    m_erasePage = Flash::Device::SectorAtAddress(eraseAddress);
+  } else if (eraseAddress >= k_externalFlashStartAddress && eraseAddress <= k_externalFlashEndAddress) {
+    m_erasePage = Flash::Device::NumberOfSectors + ExternalFlash::Device::SectorAtAddress(eraseAddress - k_externalFlashStartAddress);
+  } else {
     // Unrecognized sector
     m_state = State::dfuERROR;
     m_status = Status::errTARGET;
@@ -201,10 +204,13 @@ void DFUInterface::eraseMemoryIfNeeded() {
     return;
   }
 
-  if (m_erasePage == Ion::Flash::Device::NumberOfSectors) {
+  if (m_erasePage == Flash::Device::NumberOfSectors + ExternalFlash::Device::NumberOfSectors) {
     Flash::Device::MassErase();
-  } else {
+    ExternalFlash::Device::MassErase();
+  } else if (m_erasePage < Flash::Device::NumberOfSectors) {
     Flash::Device::EraseSector(m_erasePage);
+  } else {
+    ExternalFlash::Device::EraseSector(m_erasePage - Flash::Device::NumberOfSectors);
   }
 
   /* Put an out of range value in m_erasePage to indicate that no erase is
@@ -222,6 +228,8 @@ void DFUInterface::writeOnMemory() {
     // Write on SRAM
     // FIXME We should check that we are not overriding the current instructions.
     memcpy((void *)m_writeAddress, m_largeBuffer, m_largeBufferLength);
+  } else if (m_writeAddress >= k_externalFlashStartAddress && m_writeAddress <= k_externalFlashEndAddress) {
+    ExternalFlash::Device::WriteMemory(m_largeBuffer, reinterpret_cast<uint8_t *>(m_writeAddress) - k_externalFlashStartAddress, m_largeBufferLength);
   } else {
     // Invalid write address
     m_largeBufferLength = 0;
diff --git a/ion/src/device/usb/dfu_interface.h b/ion/src/device/usb/dfu_interface.h
index 6284ce951..7fce4bf40 100644
--- a/ion/src/device/usb/dfu_interface.h
+++ b/ion/src/device/usb/dfu_interface.h
@@ -130,6 +130,8 @@ private:
   constexpr static uint32_t k_flashEndAddress = 0x08100000;
   constexpr static uint32_t k_sramStartAddress = 0x20000000;
   constexpr static uint32_t k_sramEndAddress = 0x20040000;
+  constexpr static uint32_t k_externalFlashStartAddress = 0x90000000;
+  constexpr static uint32_t k_externalFlashEndAddress = 0x90800000;
 
   // Download and upload
   bool processDownloadRequest(uint16_t wLength, uint16_t * transferBufferLength);