diff --git a/tools/valgrind-webrtc/webrtc_tests.py b/tools/valgrind-webrtc/webrtc_tests.py
index 2c2eeed9d..801f1e1ac 100755
--- a/tools/valgrind-webrtc/webrtc_tests.py
+++ b/tools/valgrind-webrtc/webrtc_tests.py
@@ -90,7 +90,7 @@ def main(_):
   parser = optparse.OptionParser(
       'usage: %prog -b <dir> -t <test> -- <test args>')
   parser.disable_interspersed_args()
-  parser.add_option('-b', '--build_dir',
+  parser.add_option('-b', '--build-dir',
                     help=('Location of the compiler output. Can only be used '
                           'when the test argument does not contain this path.'))
   parser.add_option("--target", help="Debug or Release")