diff --git a/src/install.sh b/src/install.sh
index 11602ce..46b0631 100644
--- a/src/install.sh
+++ b/src/install.sh
@@ -105,6 +105,7 @@ findFile() {
 }
 
 USER_PORTS="22,80,443,445,${USER_PORTS:-}"
+[ -z "${DISK_FMT:-}" ] && DISK_FMT="qcow2"
 
 if ! makeDir "$STORAGE"; then
   error "Failed to create directory \"$STORAGE\" !" && exit 33