diff --git a/osbase/build/mkimage/def.bzl b/osbase/build/mkimage/def.bzl
index 3f9327b..33323d7 100644
--- a/osbase/build/mkimage/def.bzl
+++ b/osbase/build/mkimage/def.bzl
@@ -1,22 +1,30 @@
 def _node_image_impl(ctx):
     img_file = ctx.actions.declare_file(ctx.label.name + ".img")
+
+    arguments = ctx.actions.args()
+    arguments.add_all([
+        "-efi",
+        ctx.file.kernel.path,
+        "-system",
+        ctx.file.system.path,
+        "-abloader",
+        ctx.file.abloader.path,
+        "-out",
+        img_file.path,
+    ])
+
+    if len(ctx.files.bios_bootcode) != 0:
+        arguments.add_all(["-bios_bootcode", ctx.file.bios_bootcode.path])
+
     ctx.actions.run(
         mnemonic = "MkImage",
         executable = ctx.executable._mkimage,
-        arguments = [
-            "-efi",
-            ctx.file.kernel.path,
-            "-system",
-            ctx.file.system.path,
-            "-abloader",
-            ctx.file.abloader.path,
-            "-out",
-            img_file.path,
-        ],
+        arguments = [arguments],
         inputs = [
             ctx.file.kernel,
             ctx.file.system,
             ctx.file.abloader,
+            ctx.file.bios_bootcode,
         ],
         outputs = [img_file],
     )
@@ -45,6 +53,14 @@
             mandatory = True,
             allow_single_file = True,
         ),
+        "bios_bootcode": attr.label(
+            doc = """
+            Optional label to the BIOS bootcode which gets placed at the start of the first block of the image.
+            Limited to 440 bytes, padding is not required. It is only used by legacy BIOS boot.
+        """,
+            mandatory = False,
+            allow_single_file = True,
+        ),
         "_mkimage": attr.label(
             doc = "The mkimage executable.",
             default = "//osbase/build/mkimage",