diff --git a/projects/implicitron_trainer/tests/experiment.yaml b/projects/implicitron_trainer/tests/experiment.yaml
index 267dd5c3..eda38f3a 100644
--- a/projects/implicitron_trainer/tests/experiment.yaml
+++ b/projects/implicitron_trainer/tests/experiment.yaml
@@ -201,7 +201,7 @@ generic_model_args:
     bias: 1.0
     skip_in: []
     weight_norm: true
-    n_harmonic_functions_xyz: -1
+    n_harmonic_functions_xyz: 0
     pooled_feature_dim: 0
     encoding_dim: 0
   implicit_function_NeRFormerImplicitFunction_args:
diff --git a/pytorch3d/implicitron/models/implicit_function/idr_feature_field.py b/pytorch3d/implicitron/models/implicit_function/idr_feature_field.py
index 19d3b39d..31e022f6 100644
--- a/pytorch3d/implicitron/models/implicit_function/idr_feature_field.py
+++ b/pytorch3d/implicitron/models/implicit_function/idr_feature_field.py
@@ -58,7 +58,7 @@ class IdrFeatureField(ImplicitFunctionBase, torch.nn.Module):
     bias: float = 1.0
     skip_in: Sequence[int] = ()
     weight_norm: bool = True
-    n_harmonic_functions_xyz: int = -1
+    n_harmonic_functions_xyz: int = 0
     pooled_feature_dim: int = 0
     encoding_dim: int = 0
 
diff --git a/tests/implicitron/test_srn.py b/tests/implicitron/test_srn.py
index 367ec41e..48b71bf1 100644
--- a/tests/implicitron/test_srn.py
+++ b/tests/implicitron/test_srn.py
@@ -69,6 +69,7 @@ class TestSRN(TestCaseMixin, unittest.TestCase):
         )
         self.assertIsNone(rays_colors)
 
+    @torch.no_grad()
     def test_lstm(self):
         args = get_default_args(GenericModel)
         args.render_image_height = 80
@@ -80,12 +81,31 @@ class TestSRN(TestCaseMixin, unittest.TestCase):
         args.raysampler_NearFarRaySampler_args.n_pts_per_ray_evaluation = 1
         args.renderer_LSTMRenderer_args.bg_color = [0.4, 0.4, 0.2]
         gm = GenericModel(**args)
+
         camera = PerspectiveCameras()
-        gm.forward(
+        image = gm.forward(
             camera=camera,
             image_rgb=None,
             fg_probability=None,
             sequence_name="",
             mask_crop=None,
             depth_map=None,
-        )
+        )["images_render"]
+        self.assertEqual(image.shape, (1, 3, 80, 80))
+        self.assertGreater(image.max(), 0.8)
+
+        # Force everything to be background
+        pixel_generator = gm._implicit_functions[0]._fn.pixel_generator
+        pixel_generator._density_layer.weight.zero_()
+        pixel_generator._density_layer.bias.fill_(-1.0e6)
+
+        image = gm.forward(
+            camera=camera,
+            image_rgb=None,
+            fg_probability=None,
+            sequence_name="",
+            mask_crop=None,
+            depth_map=None,
+        )["images_render"]
+        self.assertConstant(image[:, :2], 0.4)
+        self.assertConstant(image[:, 2], 0.2)