diff --git a/tools/pkg_war.bzl b/tools/pkg_war.bzl
index 461c5c5..ce094ff 100644
--- a/tools/pkg_war.bzl
+++ b/tools/pkg_war.bzl
@@ -61,6 +61,7 @@
         elif hasattr(l, "files"):
             transitive_libs.append(l.files)
 
+    transitive_lib_deps = depset(transitive = transitive_libs)
     for dep in transitive_lib_deps.to_list():
         cmd = cmd + _add_file(ctx.attr.name, dep, build_output + "/WEB-INF/lib/")
         inputs.append(dep)