diff --git a/phygnn/layers/custom_layers.py b/phygnn/layers/custom_layers.py
index 712994a..d92c1d0 100644
--- a/phygnn/layers/custom_layers.py
+++ b/phygnn/layers/custom_layers.py
@@ -897,6 +897,50 @@ def call(x, hi_res_adder):
         return x + hi_res_adder
 
 
+class Sup3rFixer(tf.keras.layers.Layer):
+    """Layer to fix certain values for a sup3r model in the middle of a
+    super resolution forward pass. This is used to condition models on sparse
+    observation data."""
+
+    def __init__(self, name=None):
+        """
+        Parameters
+        ----------
+        name : str | None
+            Unique str identifier of the fixer layer. Usually the name of the
+            hi-resolution feature used in the fixing.
+        """
+        super().__init__(name=name)
+
+    @staticmethod
+    def call(x, hi_res_fixer, feature_index):
+        """Fixes hi-resolution data for the tensor x in the middle of a
+        sup3r resolution network.
+
+        Parameters
+        ----------
+        x : tf.Tensor
+            Input tensor
+        hi_res_fixer : tf.Tensor | np.ndarray
+            This should be a 4D array for spatial enhancement model or 5D array
+            for a spatiotemporal enhancement model (obs, spatial_1, spatial_2,
+            (temporal), 1) that can be used to fix values of x.
+        feature_index : int
+            The index of the feature to fix. This assumes that x has the same
+            number of channels and indexing as the model output features.
+
+        Returns
+        -------
+        x : tf.Tensor
+            Output tensor with the hi_res_fixer used to fix values of x.
+        """
+        mask = tf.math.is_nan(hi_res_fixer[..., 0])
+        arrs = [x[..., i] for i in range(x.shape[-1])]
+        arrs[feature_index] = tf.where(
+            mask, x[..., feature_index], hi_res_fixer[..., 0])
+        return tf.stack(arrs, axis=-1)
+
+
 class Sup3rConcat(tf.keras.layers.Layer):
     """Layer to concatenate a high-resolution feature to a sup3r model in the
     middle of a super resolution forward pass."""
diff --git a/tests/test_layers.py b/tests/test_layers.py
index 10758de..064c948 100644
--- a/tests/test_layers.py
+++ b/tests/test_layers.py
@@ -3,25 +3,27 @@
 """
 import os
 from tempfile import TemporaryDirectory
+
 import numpy as np
 import pytest
 import tensorflow as tf
 
+from phygnn import TfModel
 from phygnn.layers.custom_layers import (
     ExpandDims,
     FlattenAxis,
+    FunctionalLayer,
+    GaussianAveragePooling2D,
     GaussianNoiseAxis,
+    LogTransform,
+    SigLin,
     SkipConnection,
     SpatioTemporalExpansion,
+    Sup3rFixer,
     TileLayer,
-    FunctionalLayer,
-    GaussianAveragePooling2D,
-    SigLin,
-    LogTransform,
     UnitConversion,
 )
 from phygnn.layers.handlers import HiddenLayers, Layers
-from phygnn import TfModel
 
 
 @pytest.mark.parametrize(
@@ -224,7 +226,7 @@ def test_temporal_depth_to_time(t_mult, s_mult, t_roll):
                                     t_roll=t_roll)
     n_filters = 2 * s_mult**2 * t_mult
     shape = (1, 4, 4, 3, n_filters)
-    n = np.product(shape)
+    n = np.prod(shape)
     x = np.arange(n).reshape(shape)
     y = layer(x)
     assert y.shape[0] == x.shape[0]
@@ -622,3 +624,22 @@ def test_unit_conversion():
         # bad number of scalar values
         layer = UnitConversion(adder=0, scalar=[100, 1, 1])
         y = layer(x)
+
+
+def test_fixer_layer():
+    """Make sure ``Sup3rFixer`` layer works properly"""
+    x = np.random.uniform(0, 1, (1, 10, 10, 4)).astype(np.float32)
+    y = np.random.uniform(0, 1, (1, 10, 10, 1)).astype(np.float32)
+    mask = np.random.choice([False, True], (1, 10, 10), p=[0.1, 0.9])
+    y[mask] = np.nan
+
+    x = tf.convert_to_tensor(x)
+    y = tf.convert_to_tensor(y)
+
+    layer = Sup3rFixer()
+    out = layer(x, y, feature_index=0).numpy()
+
+    assert tf.reduce_any(tf.math.is_nan(y))
+    assert np.allclose(out[..., 0][~mask], y[..., 0][~mask])
+    assert x.shape == out.shape
+    assert not tf.reduce_any(tf.math.is_nan(out))