diff --git a/src/install.sh b/src/install.sh
index 57d3d67..f480f8d 100644
--- a/src/install.sh
+++ b/src/install.sh
@@ -9,9 +9,11 @@ detect () {
 
   dir=$(isoinfo -f -i "$file")
 
-  # Automaticly detect UEFI-compatible ISO's
-  if echo "${dir^^}" | grep -q "^/EFI"; then
-    [ -z "${BOOT_MODE:-}" ] && BOOT_MODE="uefi"
+  if [ -z "${BOOT_MODE:-}" ]; then
+    # Automaticly detect UEFI-compatible ISO's
+    dir=$(isoinfo -f -i "$file")
+    dir=$(echo "${dir^^}" | grep "^/EFI")
+    [ -n "$dir" ] && BOOT_MODE="uefi"
   fi
 
   BOOT="$file"