diff --git a/tools/js.bzl b/tools/js.bzl
index 94c11e1..daafe16 100644
--- a/tools/js.bzl
+++ b/tools/js.bzl
@@ -131,20 +131,20 @@
 )
 
 def _bower_component_impl(ctx):
-    transitive_zipfiles = depset([ctx.file.zipfile])
-    for d in ctx.attr.deps:
-        transitive_zipfiles += d.transitive_zipfiles
+    transitive_zipfiles = depset(
+        direct = [ctx.file.zipfile],
+        transitive = [d.transitive_zipfiles for d in ctx.attr.deps],
+    )
 
-    transitive_licenses = depset()
-    if ctx.file.license:
-        transitive_licenses += depset([ctx.file.license])
+    transitive_licenses = depset(
+        direct = [ctx.file.license],
+        transitive = [d.transitive_licenses for d in ctx.attr.deps],
+    )
 
-    for d in ctx.attr.deps:
-        transitive_licenses += d.transitive_licenses
-
-    transitive_versions = depset(ctx.files.version_json)
-    for d in ctx.attr.deps:
-        transitive_versions += d.transitive_versions
+    transitive_versions = depset(
+        direct = ctx.files.version_json,
+        transitive = [d.transitive_versions for d in ctx.attr.deps],
+    )
 
     return struct(
         transitive_licenses = transitive_licenses,
@@ -183,12 +183,12 @@
         mnemonic = "GenBowerZip",
     )
 
-    licenses = depset()
+    licenses = []
     if ctx.file.license:
-        licenses += depset([ctx.file.license])
+        licenses.append(ctx.file.license)
 
     return struct(
-        transitive_licenses = licenses,
+        transitive_licenses = depset(licenses),
         transitive_versions = depset(),
         transitive_zipfiles = list([ctx.outputs.zip]),
     )
@@ -233,15 +233,16 @@
     """A bunch of bower components zipped up."""
     zips = depset()
     for d in ctx.attr.deps:
-        zips += d.transitive_zipfiles
+        files = d.transitive_zipfiles
 
-    versions = depset()
-    for d in ctx.attr.deps:
-        versions += d.transitive_versions
+        # TODO(davido): Make sure the field always contains a depset
+        if type(files) == "list":
+            files = depset(files)
+        zips = depset(transitive = [zips, files])
 
-    licenses = depset()
-    for d in ctx.attr.deps:
-        licenses += d.transitive_versions
+    versions = depset(transitive = [d.transitive_versions for d in ctx.attr.deps])
+
+    licenses = depset(transitive = [d.transitive_versions for d in ctx.attr.deps])
 
     out_zip = ctx.outputs.zip
     out_versions = ctx.outputs.version_json
@@ -303,7 +304,7 @@
     else:
         bundled = ctx.outputs.html
     destdir = ctx.outputs.html.path + ".dir"
-    zips = [z for d in ctx.attr.deps for z in d.transitive_zipfiles]
+    zips = [z for d in ctx.attr.deps for z in d.transitive_zipfiles.to_list()]
 
     hermetic_npm_binary = " ".join([
         "python",