diff --git a/niar/build.py b/niar/build.py
index 1918459..06f455d 100644
--- a/niar/build.py
+++ b/niar/build.py
@@ -79,7 +79,7 @@ def main(np: Project, args):
             products = plan.execute_local(f"build/{subdir}")
 
         # This is specific to toolchains that use Yosys, but I'm unlikely to use anything else ...
-        deps = [f"{np.name}.il", f"{np.name}.ys"]
+        deps = [f"{np.name}.il", f"{np.name}.ys"] + np.externals
         cr.add_process(execute_build,
             infs=[{np.path.build(subdir, fn): plan.files[fn] for fn in deps}],
             outf=np.path.build(subdir, np.name))