diff --git a/scripts/lib/custom-docker-build b/scripts/lib/custom-docker-build
index 5e78593..1d1bcb3 100755
--- a/scripts/lib/custom-docker-build
+++ b/scripts/lib/custom-docker-build
@@ -389,7 +389,14 @@ function build_custom_if_needed() {
     printf "\n\nSUCCESS - Successfully built:\n\t%s\n" "$full_image_name"
 }
 
-# Use DEBIAN by default unless specified otherwise
-DEBIAN=${DEBIAN:-bullseye}
+# If OS is specified ignore other ways to specify system
+# Use DEBIAN if UBI is not specified
+if [[ -n "$OS" ]]; then
+    unset DEBIAN UBI
+elif [[ -n "$UBI" ]]; then
+    unset DEBIAN
+else
+    DEBIAN=${DEBIAN:-bullseye}
+fi
 
 build_custom_if_needed $@