diff --git a/nerfstudio/data/datamanagers/full_images_datamanager.py b/nerfstudio/data/datamanagers/full_images_datamanager.py
index 6e041b33d..47925acce 100644
--- a/nerfstudio/data/datamanagers/full_images_datamanager.py
+++ b/nerfstudio/data/datamanagers/full_images_datamanager.py
@@ -387,6 +387,8 @@ def _undistort_image(
                 mask = cv2.undistort(mask, K, distortion_params, None, newK)  # type: ignore
             mask = mask[y : y + h, x : x + w]
             mask = torch.from_numpy(mask).bool()
+            if len(mask.shape) == 2:
+                mask = mask[:, :, None]
         K = newK
 
     elif camera.camera_type.item() == CameraType.FISHEYE.value:
@@ -406,6 +408,8 @@ def _undistort_image(
             mask = mask.astype(np.uint8) * 255
             mask = cv2.fisheye.undistortImage(mask, K, distortion_params, None, newK)
             mask = torch.from_numpy(mask).bool()
+            if len(mask.shape) == 2:
+                mask = mask[:, :, None]
         K = newK
     elif camera.camera_type.item() == CameraType.FISHEYE624.value:
         fisheye624_params = torch.cat(
@@ -498,6 +502,8 @@ def _undistort_image(
             )
             / 255.0
         ).bool()[..., None]
+        if len(mask.shape) == 2:
+            mask = mask[:, :, None]
         assert mask.shape == (undist_h, undist_w, 1)
         K = undist_K.numpy()
     else: