diff --git a/dap/algos/mask.py b/dap/algos/mask.py
index 1ed79fa..0015d49 100644
--- a/dap/algos/mask.py
+++ b/dap/algos/mask.py
@@ -2,8 +2,10 @@ import numpy as np
 
 
 def calc_mask_pixels(pfdata, pixel_mask_pf):
-    if pixel_mask_pf is not None:
-        pfdata[pixel_mask_pf != 1] = np.nan #TODO: boolean mask
+    if pixel_mask_pf is None:
+        return
+
+    pfdata[pixel_mask_pf != 1] = np.nan #TODO: boolean mask