--- a/python/mozbuild/mozbuild/frontend/gyp_reader.py
+++ b/python/mozbuild/mozbuild/frontend/gyp_reader.py
@@ -88,16 +88,17 @@ def read_from_gyp(config, path, output, 
     # unicode strings, so convert them.
     path = encode(path)
     str_vars = dict((name, encode(value)) for name, value in vars.items())
 
     params = {
         b'parallel': False,
         b'generator_flags': {},
         b'build_files': [path],
+        b'root_targets': None,
     }
 
     # Files that gyp_chromium always includes
     includes = [encode(mozpath.join(script_dir, 'common.gypi'))]
     finder = FileFinder(chrome_src, find_executables=False)
     includes.extend(encode(mozpath.join(chrome_src, name))
         for name, _ in finder.find('*/supplement.gypi'))