diff --git a/scripts/lib/custom-docker-build b/scripts/lib/custom-docker-build
index 1c8292d..9a003cc 100755
--- a/scripts/lib/custom-docker-build
+++ b/scripts/lib/custom-docker-build
@@ -13,6 +13,16 @@ function get_base_image_reference() {
     fi
 }
 
+function print_os_args() {
+    CUSTOM_BASE_IMAGE=get_base_image_reference "$1"
+
+    if [ -z "$CUSTOM_BASE_IMAGE" ]; then
+        CUSTOM_BASE_IMAGE="$CUSTOM_DOCKER_ARCH/debian:buster"
+    fi
+
+    printf -- "--build-arg CUSTOM_BASE_IMAGE=%s " "$CUSTOM_BASE_IMAGE"
+}
+
 function print_golang_args() {
     declare -A GOLANG_DOWNLOAD_SHA256
 
@@ -334,7 +344,7 @@ function parse_arguments() {
             version="${!tool}"
             case "$tool" in
                 ARCH) CUSTOM_DOCKER_ARCH=$version ;;
-                OS) CUSTOM_BASE_IMAGE=get_base_image_reference $version ;;
+                OS) print_os_args $version ;;
                 RUBY) print_ruby_args $version ;;
                 BUNDLER) print_bundler_args $version ;;
                 RUBYGEMS) print_rubygems_args $version ;;
@@ -357,12 +367,6 @@ function parse_arguments() {
             esac
         fi
     done
-
-    if [ -z "$CUSTOM_BASE_IMAGE" ]; then
-        CUSTOM_BASE_IMAGE="$CUSTOM_DOCKER_ARCH/debian:buster"
-    fi
-
-    printf -- "--build-arg CUSTOM_BASE_IMAGE=%s " "$CUSTOM_BASE_IMAGE"
 }
 
 function generate_command() {