diff --git a/ChangeLog b/ChangeLog
index 8a24f1c..5e0493a 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,7 @@
 2017-10-03  NIIBE Yutaka  <gniibe@fsij.org>
 
+	* src/Makefile (build/flash.data): Generate.
+
 	* src/main.c (flash_addr_key_storage_start)
 	(flash_addr_data_storage_start): New.
 	(main): Determine flash address.
diff --git a/src/Makefile b/src/Makefile
index da36faa..1e21543 100644
--- a/src/Makefile
+++ b/src/Makefile
@@ -75,3 +75,14 @@ build/bignum.o: OPT = -O3 -g
 distclean: clean
 	-rm -f gnuk.ld config.h board.h config.mk \
 	       usb-strings.c.inc usb-vid-pid-ver.c.inc
+
+ifneq ($(EMULATION),)
+build/flash.data: Makefile
+	@echo 'Generating 8192-byte flash.data'
+	@/bin/echo -n -e '\xff\xff\xff\xff\xff\xff\xff\xff' >$@
+	@for i in $(shell seq 511); \
+	   do /bin/echo -n -e '\xff\xff\xff\xff\xff\xff\xff\xff' >>$@; done
+	@/bin/echo -n -e '\x00\x00\xff\xff\xff\xff\xff\xff' >>$@
+	@for i in $(shell seq 511); \
+	   do /bin/echo -n -e '\xff\xff\xff\xff\xff\xff\xff\xff' >>$@; done
+endif