diff --git a/ion/src/device/usb/Makefile b/ion/src/device/usb/Makefile
index fafc1a44a..361ffadc1 100644
--- a/ion/src/device/usb/Makefile
+++ b/ion/src/device/usb/Makefile
@@ -33,6 +33,8 @@ usb_objs += liba/src/memset.o
 usb_objs += liba/src/memcpy.o
 usb_objs += libaxx/src/cxxabi/pure_virtual.o
 usb_objs += ion/src/device/usb/boot.o
+usb_objs += ion/src/device/keyboard.o
+usb_objs += ion/src/device/device.o
 
 ion/src/device/usb/dfu.elf: LDFLAGS = --gc-sections -T ion/src/device/boot/dfu.ld
 ion/src/device/usb/dfu.elf: $(usb_objs)
diff --git a/ion/src/device/usb/calculator.cpp b/ion/src/device/usb/calculator.cpp
index a5449ac0f..c63262d0a 100644
--- a/ion/src/device/usb/calculator.cpp
+++ b/ion/src/device/usb/calculator.cpp
@@ -1,5 +1,6 @@
 #include "calculator.h"
 #include "../regs/regs.h"
+#include <ion/keyboard.h>
 
 namespace Ion {
 namespace USB {
@@ -11,7 +12,9 @@ void Calculator::Poll() {
   }
 
   Calculator c;
-  while (true) {
+  // Leave DFU mode when pressing the Back key.
+  // TODO also leave on detach or when unplugging
+  while (!Ion::Keyboard::scan().keyDown(Ion::Keyboard::Key::A6)) {
     c.poll();
   }
 }