diff --git a/mattport/nerf/modules/render_heads.py b/mattport/nerf/modules/render_heads.py
index 5efdceec1..1c2b5f114 100644
--- a/mattport/nerf/modules/render_heads.py
+++ b/mattport/nerf/modules/render_heads.py
@@ -12,7 +12,7 @@ from mattport.nerf.modules.module import Module
 class RenderHead(Module):
     """Base Render head"""
 
-    def __init__(self, in_dim: int, out_dim: int, activation: Optional[nn.Module]) -> None:
+    def __init__(self, in_dim: int, out_dim: int, activation: Optional[nn.Module] = None) -> None:
         """
         Args:
             in_dim (int): input dimension
@@ -30,6 +30,7 @@ class RenderHead(Module):
         layers = [nn.Linear(self.in_dim, self.out_dim)]
         if self.activation:
             layers.append(self.activation)
+        print(layers)
         self.net = nn.Sequential(*layers)
 
     def forward(self, in_tensor: TensorType[..., "in_dim"]) -> TensorType[..., "out_dim"]:
@@ -49,12 +50,12 @@ class RenderHead(Module):
 class DensityHead(RenderHead):
     """Density head"""
 
-    def __init__(self, in_dim: int, activation: Optional[nn.Module] = nn.Softplus) -> None:
+    def __init__(self, in_dim: int, activation: Optional[nn.Module] = nn.Softplus()) -> None:
         super().__init__(in_dim, 1, activation)
 
 
 class RGBHead(RenderHead):
     """RGB head"""
 
-    def __init__(self, in_dim: int, activation: Optional[nn.Module] = nn.Sigmoid) -> None:
+    def __init__(self, in_dim: int, activation: Optional[nn.Module] = nn.Sigmoid()) -> None:
         super().__init__(in_dim, 3, activation)
diff --git a/tests/nerf/modules/test_render_heads.py b/tests/nerf/modules/test_render_heads.py
index 0f5f4b7dd..b22c48499 100644
--- a/tests/nerf/modules/test_render_heads.py
+++ b/tests/nerf/modules/test_render_heads.py
@@ -1,18 +1,56 @@
 """
 Render Head Tests
 """
+import pytest
+import torch
+from torch import nn
+
 from mattport.nerf.modules import render_heads
 
 
+def test_render_head():
+    """Test rgb render head"""
+    in_dim = 6
+    out_dim = 4
+    activation = nn.ReLU()
+    render_head = render_heads.RenderHead(in_dim=in_dim, out_dim=out_dim, activation=activation)
+    assert render_head.get_out_dim() == out_dim
+
+    x = torch.ones((9, in_dim))
+
+    with pytest.raises(SystemError):
+        render_head(x)
+    render_head.build_nn_modules()
+    y = render_head(x)
+
+    assert y.shape[-1] == out_dim
+
+
 def test_density_head():
     """Test rgb render head"""
     in_dim = 6
     density_head = render_heads.DensityHead(in_dim)
     assert density_head.get_out_dim() == 1
 
+    x = torch.ones((9, in_dim))
+    with pytest.raises(SystemError):
+        density_head(x)
+    density_head.build_nn_modules()
+    y = density_head(x)
+
+    assert y.shape[-1] == 1
+
 
 def test_rgb_head():
     """Test rgb render head"""
     in_dim = 6
     rgb_head = render_heads.RGBHead(in_dim)
     assert rgb_head.get_out_dim() == 3
+
+    x = torch.ones((9, in_dim))
+    with pytest.raises(SystemError):
+        rgb_head(x)
+    rgb_head.build_nn_modules()
+    y = rgb_head(x)
+
+    assert y.shape[-1] == 3