diff --git a/gprMax/gprMax.py b/gprMax/gprMax.py
index d603e1e9..fd48e82c 100644
--- a/gprMax/gprMax.py
+++ b/gprMax/gprMax.py
@@ -38,7 +38,7 @@ def run(
     restart=None,
     mpi=False,
     gpu=None,
-    subgrid=None,
+    subgrid=False,
     autotranslate=False,
     geometry_only=False,
     geometry_fixed=False,