diff --git a/extra_data/components.py b/extra_data/components.py
index 00466cc0..d252764c 100644
--- a/extra_data/components.py
+++ b/extra_data/components.py
@@ -968,6 +968,7 @@ def ndarray(self, *, module_gaps=False, **kwargs):
         # Load mask first: it shrinks from 4 bytes/px to 1, so peak memory use
         # is lower than loading it after the data
         mask = self._load_mask(module_gaps=module_gaps)
+        print(mask[0, 0, 0, :35])
 
         data = super().ndarray(module_gaps=module_gaps, **kwargs)
         data[mask] = self._masked_value
diff --git a/extra_data/tests/make_examples.py b/extra_data/tests/make_examples.py
index 12a36b23..961bd12f 100644
--- a/extra_data/tests/make_examples.py
+++ b/extra_data/tests/make_examples.py
@@ -326,6 +326,12 @@ def make_reduced_spb_run(dir_path, raw=True, rng=None, format_version='0.5'):
                          frames_per_train=frame_counts)
             ], ntrains=64, chunksize=32, format_version=format_version)
 
+        if modno == 9 and not raw:
+            # For testing masked_data
+            with h5py.File(path, 'a') as f:
+                mask_ds = f['INSTRUMENT/SPB_DET_AGIPD1M-1/DET/9CH0:xtdf/image/mask']
+                mask_ds[0, 0, :32] = np.arange(32)
+
     write_file(osp.join(dir_path, '{}-R0238-DA01-S00000.h5'.format(prefix)),
                [ XGM('SA1_XTD2_XGM/DOOCS/MAIN'),
                  XGM('SPB_XTD9_XGM/DOOCS/MAIN'),
@@ -408,6 +414,10 @@ def make_fxe_jungfrau_run(dir_path):
     write_file(path, [
         JUNGFRAUModule(f'FXE_XAD_JF500K/DET/JNGFR03')
     ], ntrains=100, chunksize=1, format_version='1.0')
+    with h5py.File(path, 'a') as f:
+        # For testing masked_data
+        mask_ds = f['INSTRUMENT/FXE_XAD_JF500K/DET/JNGFR03:daqOutput/data/mask']
+        mask_ds[0, 0, 0, :32] = np.arange(32)
 
     write_file(osp.join(dir_path, f'RAW-R0052-JNGFRCTRL00-S00000.h5'), [
         JUNGFRAUControl('FXE_XAD_JF1M/DET/CONTROL'),
diff --git a/extra_data/tests/test_components.py b/extra_data/tests/test_components.py
index db771143..cc607375 100644
--- a/extra_data/tests/test_components.py
+++ b/extra_data/tests/test_components.py
@@ -252,6 +252,59 @@ def test_jungfraus_first_modno(mock_jungfrau_run, mock_fxe_jungfrau_run):
         assert np.all(arr['module'] == [modno])
 
 
+def test_jungfrau_masked_data(mock_fxe_jungfrau_run):
+    run = RunDirectory(mock_fxe_jungfrau_run)
+    jf = JUNGFRAU(run, 'FXE_XAD_JF500K')
+
+    # Default options
+    kd = jf.masked_data().select_trains(np.s_[:1])
+    arr = kd.ndarray()
+    assert arr.shape == (1, 1, 16, 512, 1024)
+    line0 = np.zeros(1024, dtype=np.float32)
+    line0[1:32] = np.nan
+    np.testing.assert_array_equal(arr[0, 0, 0, 0, :], line0, strict=True)
+
+    # Xarray
+    xarr = kd.xarray()
+    assert xarr.dims[:2] == ('module', 'trainId')
+    np.testing.assert_array_equal(xarr.values[0, 0, 0, 0, :], line0, strict=True)
+
+    # Specify which mask bits to use, & replace masked values with 99
+    kd = jf.masked_data(mask_bits=1, masked_value=99).select_trains(np.s_[:1])
+    arr = kd.ndarray()
+    assert arr.shape == (1, 1, 16, 512, 1024)
+    line0 = np.zeros(1024, dtype=np.float32)
+    line0[1:32:2] = 99
+    np.testing.assert_array_equal(arr[0, 0, 0, 0, :], line0, strict=True)
+
+    # Different field
+    kd = jf.masked_data('data.gain', masked_value=255).select_trains(np.s_[:1])
+    arr = kd.ndarray()
+    assert arr.shape == (1, 1, 16, 512, 1024)
+    line0 = np.zeros(1024, dtype=np.uint8)
+    line0[1:32] = 255
+    np.testing.assert_array_equal(arr[0, 0, 0, 0, :], line0, strict=True)
+
+
+def test_xtdf_masked_data(mock_reduced_spb_proc_run):
+    run = RunDirectory(mock_reduced_spb_proc_run)
+    agipd = AGIPD1M(run, modules=[8, 9])
+
+    kd = agipd.masked_data().select_trains(np.s_[:1])
+    assert kd.shape == (2, kd.shape[1], 512, 128)
+    arr = kd.ndarray()
+    assert arr.shape == kd.shape
+    line0_2mod = np.zeros((2, 128), dtype=np.float32)
+    line0_2mod[1, 1:32] = np.nan
+    np.testing.assert_array_equal(arr[:, 0, 0, :], line0_2mod, strict=True)
+
+    kd = agipd.masked_data(mask_bits=1, masked_value=-1).select_trains(np.s_[:1])
+    arr = kd.ndarray()
+    line0_2mod = np.zeros((2, 128), dtype=np.float32)
+    line0_2mod[1, 1:32:2] = -1
+    np.testing.assert_array_equal(arr[:, 0, 0, :], line0_2mod, strict=True)
+
+
 def test_get_dask_array(mock_fxe_raw_run):
     run = RunDirectory(mock_fxe_raw_run)
     det = LPD1M(run)