diff --git a/build_library/vm_image_util.sh b/build_library/vm_image_util.sh
index 305b182a47..bd6093996d 100644
--- a/build_library/vm_image_util.sh
+++ b/build_library/vm_image_util.sh
@@ -48,6 +48,7 @@ IMG_DEFAULT_CONF_FORMAT=
 IMG_DEFAULT_MEM=1024
 
 ## qemu
+IMG_qemu_DISK_FORMAT=qcow2
 IMG_qemu_CONF_FORMAT=qemu
 
 ## xen
@@ -131,6 +132,7 @@ _disk_ext() {
     local disk_format=$(_get_vm_opt DISK_FORMAT)
     case ${disk_format} in
         raw) echo bin;;
+        qcow2) echo img;;
         *) echo "${disk_format}";;
     esac
 }
@@ -256,6 +258,10 @@ _write_raw_disk() {
     mv "$1" "$2"
 }
 
+_write_qcow2_disk() {
+    qemu-img convert -f raw "$1" -O qcow2 "$2"
+}
+
 _write_vmdk_disk() {
     qemu-img convert -f raw "$1" -O vmdk "$2"
 }
diff --git a/lib/cros_vm_constants.sh b/lib/cros_vm_constants.sh
index 7387a91d51..9012135bfc 100644
--- a/lib/cros_vm_constants.sh
+++ b/lib/cros_vm_constants.sh
@@ -9,7 +9,7 @@ DEFAULT_MEM="1024"
 DEFAULT_VMDK="ide.vmdk"
 DEFAULT_VMX="coreos.vmx"
 DEFAULT_VBOX_DISK="os.vdi"
-DEFAULT_QEMU_IMAGE="coreos_developer_qemu_image.bin"
+DEFAULT_QEMU_IMAGE="coreos_developer_qemu_image.img"
 
 # Minimum sizes for full size vm images -- needed for update.
 MIN_VDISK_SIZE_FULL=9216