diff --git a/pylabrobot/legacy/plate_reading/imager.py b/pylabrobot/legacy/plate_reading/imager.py
index e05b8c25d66..5df63457903 100644
--- a/pylabrobot/legacy/plate_reading/imager.py
+++ b/pylabrobot/legacy/plate_reading/imager.py
@@ -236,10 +236,9 @@ async def capture(
     if isinstance(well, tuple):
       row, column = well
     else:
-      idx = cast(Plate, well.parent).index_of_item(well)
-      if idx is None:
-        raise ValueError(f"Well {well} not in plate {well.parent}")
-      row, column = divmod(idx, cast(Plate, well.parent).num_items_x)
+      plate = cast(Plate, well.parent)
+      row = plate.get_child_row(well)
+      column = plate.get_child_column(well)
 
     if isinstance(exposure_time, AutoExposure):
       assert focal_height != "machine-auto", "Focal height must be specified for auto exposure"
diff --git a/pylabrobot/legacy/plate_reading/plate_reader_tests.py b/pylabrobot/legacy/plate_reading/plate_reader_tests.py
index bd61f1bc296..f20dc496f4e 100644
--- a/pylabrobot/legacy/plate_reading/plate_reader_tests.py
+++ b/pylabrobot/legacy/plate_reading/plate_reader_tests.py
@@ -1,8 +1,12 @@
 import unittest
 
 from pylabrobot.legacy.plate_reading import PlateReader
+from pylabrobot.legacy.plate_reading.backend import ImagerBackend
 from pylabrobot.legacy.plate_reading.chatterbox import PlateReaderChatterboxBackend
-from pylabrobot.resources import Plate
+from pylabrobot.legacy.plate_reading.imager import Imager
+from pylabrobot.legacy.plate_reading.standard import ImagingMode, ImagingResult, Objective
+from pylabrobot.resources import Coordinate, Plate
+from pylabrobot.resources.corning.plates import cor_96_wellplate_360uL_Fb
 
 
 class TestPlateReaderResource(unittest.TestCase):
@@ -35,3 +39,43 @@ def test_get_plate(self):
     self.pr.assign_child_resource(plate)
 
     self.assertEqual(self.pr.get_plate(), plate)
+
+
+class _RecordingImagerBackend(ImagerBackend):
+  """Records the (row, column) each capture is dispatched to."""
+
+  last_capture = None
+
+  async def setup(self):
+    pass
+
+  async def stop(self):
+    pass
+
+  async def capture(self, row, column, mode, objective, exposure_time, focal_height, gain, plate):
+    self.last_capture = (row, column)
+    return ImagingResult(images=[], exposure_time=10, focal_height=0)
+
+
+class TestImagerWellIndexing(unittest.IsolatedAsyncioTestCase):
+  """A Well object must resolve to the same (row, column) as the equivalent tuple."""
+
+  async def test_well_object_resolves_to_row_column(self):
+    backend = _RecordingImagerBackend()
+    imager = Imager(name="imager", size_x=1, size_y=1, size_z=1, backend=backend)
+    plate = cor_96_wellplate_360uL_Fb(name="plate")
+    imager.assign_child_resource(plate, location=Coordinate.zero())
+    await imager.setup()
+
+    # plate items are ordered column-major (A1, B1, ..., H1, A2, ...), so e.g. B2 has
+    # index 9, which must decode to row 1, column 1
+    for name, expected in [("A1", (0, 0)), ("B2", (1, 1)), ("H1", (7, 0)), ("A12", (0, 11))]:
+      await imager.capture(
+        well=plate.get_well(name),
+        mode=ImagingMode.BRIGHTFIELD,
+        objective=Objective.O_4X_PL_FL,
+        exposure_time=10,
+        focal_height=1,
+        gain=1,
+      )
+      self.assertEqual(backend.last_capture, expected)