diff --git a/EasyBuild b/EasyBuild
index 0d2a1bc..c91eeb5 100644
--- a/EasyBuild
+++ b/EasyBuild
@@ -3,3 +3,8 @@ SetDirectory "{Parent}"								# too easy
 
 Make -w > :BuildResults:BuildOut
 :BuildResults:BuildOut
+
+# So that PowerROM is definitely the newest thing in the tree!
+SetDirectory :BuildResults:
+Catenate PowerROM > PowerROM_
+Rename -y PowerROM_ PowerROM
diff --git a/EasyBuild.sh b/EasyBuild.sh
new file mode 100755
index 0000000..9419f57
--- /dev/null
+++ b/EasyBuild.sh
@@ -0,0 +1,29 @@
+#!/bin/sh
+
+# Uncomment this block to use https://github.com/elliotnunn/mac-rom
+
+# echo "> Diving into mac-rom repo"
+# cd ../mac-rom
+# ./EasyBuild.sh
+# cmp -s BuildResults/RISC/Image/RomMondo "$OLDPWD/RomMondo.bin" || cp BuildResults/RISC/Image/RomMondo "$OLDPWD/RomMondo.bin"
+# cd "$OLDPWD"
+# echo "< Done with mac-rom repo"
+
+
+# Avoid the uber-slow step of running the emulator when nothing has changed
+
+if [ ! -f BuildResults/PowerROM ]
+then
+	echo "PowerROM not yet built"
+	echo "> Starting emulator to build PowerROM"
+	empw -b EasyBuild
+	echo "< Emulator done"
+	exit
+fi
+
+echo "Checking for files updated since PowerROM"
+find **/*.s *.s *.x *.bin -newer BuildResults/PowerROM | grep . || exit 0
+
+echo "> Starting emulator to build PowerROM"
+empw -b EasyBuild
+echo "< Emulator done"
diff --git a/README.md b/README.md
index fdf71ae..72b99b2 100644
--- a/README.md
+++ b/README.md
@@ -52,8 +52,16 @@ Using EMPW, that's:
 
 	empw -b EasyBuild
 
+Even nicer is this Unix shell script, which avoids unnecessary launches of the emulator:
+
+	./EasyBuild.sh
+
 The 4 MB image will be at `BuildResults/PowerROM`.
 
+Using a different 68k ROM image
+-------------------------------
+Clone https://github.com/elliotnunn/mac-rom next door to this repo, and uncomment the "Diving into mac-rom repo" lines in `EasyBuild.sh`
+
 What's next?
 ------------
 On NewWorld Macs, this image is extracted into RAM from a "Mac OS ROM" file at boot. Use https://github.com/elliotnunn/newworld-rom to build such a file.