diff --git a/simpeg_drivers/joint/driver.py b/simpeg_drivers/joint/driver.py
index 5ad9c34b..bc93f59e 100644
--- a/simpeg_drivers/joint/driver.py
+++ b/simpeg_drivers/joint/driver.py
@@ -65,7 +65,8 @@ def data_misfit(self):
                         fun.name = f"Group_{label.upper()}:Tile_{ii}"
 
                     multipliers += [
-                        getattr(self.params, f"group_{label}_multiplier") ** 2.0
+                        (getattr(self.params, f"group_{label}_multiplier") or 1.0)
+                        ** 2.0
                     ] * len(driver.data_misfit.objfcts)
 
             if self.client:
diff --git a/simpeg_drivers/joint/joint_petrophysics/options.py b/simpeg_drivers/joint/joint_petrophysics/options.py
index ab901db0..b10816bf 100644
--- a/simpeg_drivers/joint/joint_petrophysics/options.py
+++ b/simpeg_drivers/joint/joint_petrophysics/options.py
@@ -15,6 +15,7 @@
 from typing import ClassVar
 
 from geoh5py.data import FloatData, ReferencedData
+from geoh5py.groups import SimPEGGroup
 from geoh5py.objects import Octree
 
 from simpeg_drivers import assets_path
@@ -49,6 +50,8 @@ class JointPetrophysicsOptions(BaseJointOptions):
     title: str = "Joint Petrophysically Guided Inversion (PGI)"
     inversion_type: str = "joint petrophysics"
 
+    group_a_multiplier: float | None = None
     group_b_multiplier: float | None = None
+    group_b: SimPEGGroup | None = None
     mesh: Octree
     models: JointPetrophysicsModelOptions
diff --git a/tests/run_tests/driver_joint_pgi_homogeneous_test.py b/tests/run_tests/driver_joint_pgi_homogeneous_test.py
index aff3e37d..37cea33a 100644
--- a/tests/run_tests/driver_joint_pgi_homogeneous_test.py
+++ b/tests/run_tests/driver_joint_pgi_homogeneous_test.py
@@ -143,7 +143,7 @@ def test_homogeneous_run(
         orig_data = []
         petrophysics = None
         gradient_rotation = None
-        mesh = None
+
         for suffix in "AB":
             components = SyntheticsComponents(
                 geoh5=geoh5,
@@ -226,6 +226,19 @@ def test_homogeneous_run(
                 )
                 drivers.append(MagneticInversionDriver(params))
 
+        # Test if single group is valid
+        params = JointPetrophysicsOptions.build(
+            topography_object=topography,
+            geoh5=geoh5,
+            group_a=drivers[0].out_group,
+            mesh=global_mesh,
+            petrophysical_model=petrophysics,
+        )
+        driver = JointPetrophysicsDriver(params)
+        assert len(driver.data_misfit.objfcts) == 1
+        assert driver.data_misfit.multipliers == [1.0]
+
+        # Re-build full
         params = JointPetrophysicsOptions.build(
             topography_object=topography,
             geoh5=geoh5,