diff --git a/build-bootable-rpi3-sdcard.sh b/build-bootable-rpi3-sdcard.sh
index 785877c..6ef7753 100755
--- a/build-bootable-rpi3-sdcard.sh
+++ b/build-bootable-rpi3-sdcard.sh
@@ -21,7 +21,7 @@
 
 SCRIPT_DIR=$( cd $( dirname "${BASH_SOURCE[0]}" ) && pwd)
 FUCHSIA_DIR="$SCRIPT_DIR/.."
-MINFS="$FUCHSIA_DIR/out/build-magenta/build-magenta-rpi3-arm64/tools/minfs"
+MINFS="$FUCHSIA_DIR/out/build-magenta/tools/minfs"
 MANIFEST_BUILDER="$SCRIPT_DIR/installer/manifest-builder.py"
 
 echo $FUCHSIA_DIR
@@ -32,6 +32,11 @@
 ./scripts/make-parallel magenta-rpi3-arm64
 popd > /dev/null
 
+if [[ ! -e "$MINFS" ]]; then
+  echo "minfs not found, please build fuchsia and try again."
+  exit 1
+fi
+
 lsblk
 echo "Enter the name of a block device to format: "
 echo "     This will probably be of the form 'sd[letter]', like 'sdc'"
@@ -103,6 +108,9 @@
     exit 1
 fi
 
+# Stomp the existing MBR if one exists.
+sudo dd if=/dev/zero of="$DEVICE_PATH" bs=512 count=1
+
 BOOT_PTN_OF=0
 BOOT_PTN_SZ=1024
 
@@ -182,15 +190,15 @@
 # memory as a ramfs. Building the fuchsia system in a /system partition directly
 # to the SD card reduces memory presure and alleviates the need for the RPi3's
 # bootloader to load the whole fuchsia system from the SD card to RAM upon boot.
-sudo cp "$FUCHSIA_DIR/out/build-magenta/build-magenta-rpi3-arm64/bootdata.bin" \
+sudo cp "$FUCHSIA_DIR/magenta/build-magenta-rpi3-arm64/bootdata.bin" \
         "${MOUNT_PATH}/"
 
-curl -L "https://github.com/raspberrypi/firmware/raw/master/boot/start.elf" > \
+curl -L "https://github.com/raspberrypi/firmware/raw/390f53ed0fd79df274bdcc81d99e09fa262f03ab/boot/start.elf" > \
       /tmp/start.elf
 sudo cp /tmp/start.elf "${MOUNT_PATH}/start.elf"
 rm /tmp/start.elf
 
-curl -L https://github.com/raspberrypi/firmware/raw/master/boot/bootcode.bin > \
+curl -L https://github.com/raspberrypi/firmware/raw/7fcb39cb5b5543ca7485cd1ae9e6d908f31e40c6/boot/bootcode.bin > \
      /tmp/bootcode.bin
 sudo cp /tmp/bootcode.bin "${MOUNT_PATH}/bootcode.bin"
 rm /tmp/bootcode.bin