diff --git a/docs/Bootloaders.md b/docs/Bootloaders.md
index 079ad164..77f3ad3b 100755
--- a/docs/Bootloaders.md
+++ b/docs/Bootloaders.md
@@ -195,8 +195,12 @@ SAMD21. One comes standard with the "Arduino Zero" and the other comes
 standard with the "Arduino M0".
 
 The Arduino Zero uses an 8KiB bootloader (the application must be
-compiled with a start address of 8KiB). This document does not cover
-the flashing mechanism for this bootloader.
+compiled with a start address of 8KiB). One can enter the bootloader
+by double clicking the reset button. To flash an application use
+something like:
+```
+bossac -U -p "$(FLASH_DEVICE)" --offset=0x2000 -w out/klipper.bin -v -b -R
+```
 
 The Arduino M0 uses a 16KiB bootloader (the application must be
 compiled with a start address of 16KiB). To flash an application,
diff --git a/src/samd21/Makefile b/src/samd21/Makefile
index 34de8e48..abe21013 100644
--- a/src/samd21/Makefile
+++ b/src/samd21/Makefile
@@ -42,6 +42,12 @@ $(OUT)klipper.elf.hex: $(OUT)klipper.elf
 	@echo "  Creating hex file $@"
 	$(Q)$(OBJCOPY) -j .text -j .relocate -O ihex $< $@
 
-flash: $(OUT)klipper.bin
-	@echo ""
-	@echo "  The SAMD21 build does not currently support 'make flash'"
+# Flash rules
+lib/bossac/bin/bossac:
+	@echo "  Building bossac"
+	$(Q)make -C lib/bossac bin/bossac
+
+flash: $(OUT)klipper.bin lib/bossac/bin/bossac
+	@echo "  Flashing $^ to $(FLASH_DEVICE) via bossac"
+	$(Q)if [ -z $(FLASH_DEVICE) ]; then echo "Please specify FLASH_DEVICE"; exit 1; fi
+	$(Q)lib/bossac/bin/bossac -U -p "$(FLASH_DEVICE)" --offset=0x2000 -w $(OUT)klipper.bin -v -b -R