diff --git a/src/boot.sh b/src/boot.sh
index 1b1fd07..dadf7ef 100644
--- a/src/boot.sh
+++ b/src/boot.sh
@@ -3,6 +3,7 @@ set -Eeuo pipefail
 
 # Docker environment variables
 : "${BIOS:=""}"                 # Bios file
+: "${BOOT_MODE:="legacy"}"  # Boot mode
 
 SECURE="off"
 BOOT_OPTS=""