diff --git a/util/dvsim/dvsim.py b/util/dvsim/dvsim.py
index 3f7b51e..d060f11 100755
--- a/util/dvsim/dvsim.py
+++ b/util/dvsim/dvsim.py
@@ -214,7 +214,6 @@
                         help="Print version and exit")
 
     parser.add_argument("--tool", "-t",
-                        default="",
                         help=("Explicitly set the tool to use. This is "
                               "optional for running simulations (where it can "
                               "be set in an .hjson file), but is required for "