diff --git a/prjxray/util.py b/prjxray/util.py
index 6fa10329..6fbe2bd8 100644
--- a/prjxray/util.py
+++ b/prjxray/util.py
@@ -234,3 +234,12 @@ def gen_fuzz_states(nvals):
     for i in range(nvals):
         mask = (1 << i)
         yield int(bool(bits & mask))
+
+
+def add_bool_arg(parser, yes_arg, default=False, **kwargs):
+    dashed = yes_arg.replace('--', '')
+    dest = dashed.replace('-', '_')
+    parser.add_argument(
+        yes_arg, dest=dest, action='store_true', default=default, **kwargs)
+    parser.add_argument(
+        '--no-' + dashed, dest=dest, action='store_false', **kwargs)