diff --git a/hs2p/utils/utils.py b/hs2p/utils/utils.py
index 09aee77..23d49a7 100644
--- a/hs2p/utils/utils.py
+++ b/hs2p/utils/utils.py
@@ -116,9 +116,9 @@ def load_csv(cfg):
     elif "slide_path" in df.columns:
         wsi_paths = [Path(x) for x in df.slide_path.values.tolist()]
     if "mask_path" in df.columns:
-        mask_paths = [Path(x) for x in df.mask_path.values.tolist()]
+        mask_paths = [Path(x) if x is not None and not pd.isna(x) else None for x in df.mask_path.values.tolist()]
     elif "segmentation_mask_path" in df.columns:
-        mask_paths = [Path(x) for x in df.segmentation_mask_path.values.tolist()]
+        mask_paths = [Path(x) if x is not None and not pd.isna(x) else None for x in df.segmentation_mask_path.values.tolist()]
     else:
         mask_paths = [None for _ in wsi_paths]
     return wsi_paths, mask_paths