diff --git a/src/dials/algorithms/centroid/__init__.py b/src/dials/algorithms/centroid/__init__.py
index 16f747ad69..d650f9232b 100644
--- a/src/dials/algorithms/centroid/__init__.py
+++ b/src/dials/algorithms/centroid/__init__.py
@@ -9,7 +9,7 @@ def centroid_px_to_mm(detector, scan, position, variance, sd_error):
 
     # Get the pixel to millimeter function
     assert len(detector) == 1
-    if scan.has_property("time_of_flight"):
+    if scan is not None and scan.has_property("time_of_flight"):
         return tof_centroid_px_to_mm_panel(
             detector[0], scan, position, variance, sd_error
         )
@@ -20,7 +20,7 @@ def centroid_px_to_mm_panel(panel, scan, position, variance, sd_error):
     """Convenience function to calculate centroid in mm/rad from px"""
     # Get the pixel to millimeter function
 
-    if scan.has_property("time_of_flight"):
+    if scan is not None and scan.has_property("time_of_flight"):
         return tof_centroid_px_to_mm_panel(panel, scan, position, variance, sd_error)
 
     pixel_size = panel.get_pixel_size()
@@ -75,7 +75,7 @@ def centroid_px_to_mm_panel(panel, scan, position, variance, sd_error):
 
 def tof_centroid_px_to_mm_panel(panel, scan, position, variance, sd_error):
     """Convenience function to calculate centroid in mm/tof from px"""
-    assert scan.has_property("time_of_flight")
+    assert scan is not None and scan.has_property("time_of_flight")
 
     pixel_size = panel.get_pixel_size()
     tof = scan.get_property("time_of_flight")  # (usec)
diff --git a/src/dials/algorithms/spot_finding/factory.py b/src/dials/algorithms/spot_finding/factory.py
index 7cf8400afc..becf5b8a10 100644
--- a/src/dials/algorithms/spot_finding/factory.py
+++ b/src/dials/algorithms/spot_finding/factory.py
@@ -452,6 +452,8 @@ def from_parameters(params=None, experiments=None, is_stills=False):
         # Setup the spot finder
         contains_tof_experiments = False
         for experiment in experiments:
+            if experiment.scan is None:
+                continue
             if experiment.scan.has_property("time_of_flight"):
                 contains_tof_experiments = True
             elif contains_tof_experiments: