diff --git a/bonemarketsolver/__main__.py b/bonemarketsolver/__main__.py
index 452a1c4..d3438ca 100644
--- a/bonemarketsolver/__main__.py
+++ b/bonemarketsolver/__main__.py
@@ -105,7 +105,7 @@ solver_options = parser.add_argument_group(
 
 solver_options.add_argument(
         "-v", "--verbose",
-        action='store_true',
+        action=argparse.BooleanOptionalAction,
         default=False,
         help="whether the solver should output search progress rather than showing intermediate solutions",
         dest='verbose'