--- a/build/gen_test_packages_manifest.py
+++ b/build/gen_test_packages_manifest.py
@@ -28,16 +28,21 @@ PACKAGE_SPECIFIED_HARNESSES = [
     'talos',
 ]
 
 # These packages are not present for every build configuration.
 OPTIONAL_PACKAGES = [
     'gtest',
 ]
 
+# Maps harness name to set of package names.
+EXPLICIT_HARNESSES = {
+    'web-platform': {'bin'}
+}
+
 
 def parse_args():
     parser = ArgumentParser(description='Generate a test_packages.json file to tell automation which harnesses require which test packages.')
     parser.add_argument("--common", required=True,
                         action="store", dest="tests_common",
                         help="Name of the \"common\" archive, a package to be used by all harnesses.")
     parser.add_argument("--jsshell", required=True,
                         action="store", dest="jsshell",
@@ -65,16 +70,22 @@ def generate_package_data(args):
     # harness depends on to run.
     # mozharness will use this file to determine what test zips to download,
     # which will be an optimization once parts of the main zip are split to harness
     # specific zips.
     tests_common = args.tests_common
     jsshell = args.jsshell
 
     harness_requirements = dict([(k, [tests_common, args.bin]) for k in ALL_HARNESSES])
+
+    for harness, packages in EXPLICIT_HARNESSES.items():
+        if harness in harness_requirements:
+            raise Exception('key from EXPLICIT_HARNESSES already exists: %s' % harness)
+        harness_requirements[harness] = [getattr(args, package) for package in packages]
+
     harness_requirements['jittest'].append(jsshell)
     for harness in PACKAGE_SPECIFIED_HARNESSES + OPTIONAL_PACKAGES:
         pkg_name = getattr(args, harness, None)
         if pkg_name is None:
             continue
         harness_requirements[harness].append(pkg_name)
     return harness_requirements