diff --git a/lib/iris/etc/pp_save_rules.txt b/lib/iris/etc/pp_save_rules.txt
index 8971fe6625..f8b97d4af5 100644
--- a/lib/iris/etc/pp_save_rules.txt
+++ b/lib/iris/etc/pp_save_rules.txt
@@ -761,12 +761,12 @@ THEN
 
 #MDI
 IF
-    isinstance(cm.data, ma.core.MaskedArray)
+    cm.fill_value is not None
 THEN
-    pp.bmdi = cm.data.fill_value
+    pp.bmdi = cm.fill_value
 
 IF
-    not isinstance(cm.data, ma.core.MaskedArray)
+    cm.fill_value == None
 THEN
     pp.bmdi = -1e30
 
diff --git a/lib/iris/fileformats/pp.py b/lib/iris/fileformats/pp.py
index ea921dca20..83ec3022fc 100644
--- a/lib/iris/fileformats/pp.py
+++ b/lib/iris/fileformats/pp.py
@@ -1,4 +1,4 @@
-# (C) British Crown Copyright 2010 - 2016, Met Office
+# (C) British Crown Copyright 2010 - 2017, Met Office
 #
 # This file is part of Iris.
 #
@@ -2322,6 +2322,18 @@ def as_pairs(cube, field_coords=None, target=None):
                                 target=target)
 
 
+def _data_fill_value(cube):
+    # Function to deduce a fill_value for a cube's data.
+    # This should eventually be superceded by a cube 'fill_value' property.
+    if cube.has_lazy_data():
+        fill_value = cube.lazy_data().fill_value
+    elif isinstance(cube.data, ma.MaskedArray):
+        fill_value = cube.data.fill_value
+    else:
+        fill_value = None
+    return fill_value
+
+
 def save_pairs_from_cube(cube, field_coords=None, target=None):
     """
     Use the PP saving rules (and any user rules) to convert a cube or
@@ -2404,6 +2416,11 @@ def save_pairs_from_cube(cube, field_coords=None, target=None):
 
     # Save each named or latlon slice2D in the cube
     for slice2D in cube.slices(field_coords):
+        # Attach an extra cube "fill_value" property, allowing the save rules
+        # to deduce MDI more easily without realising the data.
+        # NOTE: it is done this way because this property may exist in future.
+        slice2D.fill_value = _data_fill_value(slice2D)
+
         # Start with a blank PPField
         pp_field = PPField3()
 
@@ -2426,8 +2443,12 @@ def save_pairs_from_cube(cube, field_coords=None, target=None):
         # From UM doc F3: "Set to -99 if LBEGIN not known"
         pp_field.lbuser[1] = -99
 
-        # Set the data
-        pp_field.data = slice2D.data
+        # Set the data, keeping it lazy where possible.
+        if slice2D.has_lazy_data():
+            slice_core_data = slice2D.lazy_data()
+        else:
+            slice_core_data = slice2D.data
+        pp_field._data = slice_core_data
 
         # Run the PP save rules on the slice2D, to fill the PPField,
         # recording the rules that were used
diff --git a/lib/iris/tests/integration/test_pp.py b/lib/iris/tests/integration/test_pp.py
index 27c9d777d7..3c83202f50 100644
--- a/lib/iris/tests/integration/test_pp.py
+++ b/lib/iris/tests/integration/test_pp.py
@@ -38,6 +38,16 @@
 import iris.util
 
 
+def run_save_rules(cube, field):
+    # Add an extra "fill_value" property, as required by PP save rules, and
+    # now normally supplied by pp.save_pairs_from_cube.
+    cube.fill_value = iris.fileformats.pp._data_fill_value(cube)
+    # Ensure save rules are ready.
+    iris.fileformats.pp._ensure_save_rules_loaded()
+    # Run save rules to populate the field from the cube
+    iris.fileformats.pp._save_rules.verify(cube, field)
+
+
 class TestVertical(tests.IrisTest):
     def _test_coord(self, cube, point, bounds=None, **kwargs):
         coords = cube.coords(**kwargs)
@@ -69,8 +79,7 @@ def test_soil_level_round_trip(self):
         field.lbvc = 0
         field.brsvd = [None] * 4
         field.brlev = None
-        iris.fileformats.pp._ensure_save_rules_loaded()
-        iris.fileformats.pp._save_rules.verify(cube, field)
+        run_save_rules(cube, field)
 
         # Check the vertical coordinate is as originally specified.
         self.assertEqual(field.lbvc, 6)
@@ -103,8 +112,7 @@ def test_soil_depth_round_trip(self):
         field.lbvc = 0
         field.brlev = None
         field.brsvd = [None] * 4
-        iris.fileformats.pp._ensure_save_rules_loaded()
-        iris.fileformats.pp._save_rules.verify(cube, field)
+        run_save_rules(cube, field)
 
         # Check the vertical coordinate is as originally specified.
         self.assertEqual(field.lbvc, 6)
@@ -132,8 +140,7 @@ def test_potential_temperature_level_round_trip(self):
         field = iris.fileformats.pp.PPField3()
         field.lbfc = 0
         field.lbvc = 0
-        iris.fileformats.pp._ensure_save_rules_loaded()
-        iris.fileformats.pp._save_rules.verify(cube, field)
+        run_save_rules(cube, field)
 
         # Check the vertical coordinate is as originally specified.
         self.assertEqual(field.lbvc, 19)
@@ -197,15 +204,14 @@ def field_with_data(scale=1):
         pressure_field.lbvc = 0
         pressure_field.brsvd = [None, None]
         pressure_field.lbuser = [None] * 7
-        iris.fileformats.pp._ensure_save_rules_loaded()
-        iris.fileformats.pp._save_rules.verify(pressure_cube, pressure_field)
+        run_save_rules(pressure_cube, pressure_field)
 
         data_field = iris.fileformats.pp.PPField3()
         data_field.lbfc = 0
         data_field.lbvc = 0
         data_field.brsvd = [None, None]
         data_field.lbuser = [None] * 7
-        iris.fileformats.pp._save_rules.verify(data_cube, data_field)
+        run_save_rules(data_cube, data_field)
 
         # The reference surface field should have STASH=409
         self.assertArrayEqual(pressure_field.lbuser,
@@ -285,8 +291,7 @@ def test_hybrid_height_with_non_standard_coords(self):
         field.lbvc = 0
         field.brsvd = [None, None]
         field.lbuser = [None] * 7
-        iris.fileformats.pp._ensure_save_rules_loaded()
-        iris.fileformats.pp._save_rules.verify(cube, field)
+        run_save_rules(cube, field)
 
         self.assertEqual(field.blev, delta)
         self.assertEqual(field.brlev, delta_lower)
@@ -322,8 +327,7 @@ def test_hybrid_pressure_with_non_standard_coords(self):
         field.lbvc = 0
         field.brsvd = [None, None]
         field.lbuser = [None] * 7
-        iris.fileformats.pp._ensure_save_rules_loaded()
-        iris.fileformats.pp._save_rules.verify(cube, field)
+        run_save_rules(cube, field)
 
         self.assertEqual(field.bhlev, delta)
         self.assertEqual(field.bhrlev, delta_lower)
@@ -384,8 +388,7 @@ def field_with_data(scale=1):
         data_field.lbvc = 0
         data_field.brsvd = [None, None]
         data_field.lbuser = [None] * 7
-        iris.fileformats.pp._ensure_save_rules_loaded()
-        iris.fileformats.pp._save_rules.verify(data_cube, data_field)
+        run_save_rules(data_cube, data_field)
 
         # Check the data field has the vertical coordinate as originally
         # specified.
@@ -421,8 +424,7 @@ def convert_cube_to_field(self, cube):
         field.lbfc = 0
         field.lbvc = 0
         field.lbtim = 0
-        iris.fileformats.pp._ensure_save_rules_loaded()
-        iris.fileformats.pp._save_rules.verify(cube, field)
+        run_save_rules(cube, field)
         return field
 
     def test_time_mean_from_forecast_period(self):
@@ -608,8 +610,7 @@ def create_cube(self, longitude_coord='longitude'):
     def convert_cube_to_field(self, cube):
         field = iris.fileformats.pp.PPField3()
         field.lbvc = 0
-        iris.fileformats.pp._ensure_save_rules_loaded()
-        iris.fileformats.pp._save_rules.verify(cube, field)
+        run_save_rules(cube, field)
         return field
 
     def test_time_mean_only(self):
diff --git a/lib/iris/tests/results/cube_to_pp/append_single.txt b/lib/iris/tests/results/cube_to_pp/append_single.txt
index 642d40cb2a..6aee209281 100644
--- a/lib/iris/tests/results/cube_to_pp/append_single.txt
+++ b/lib/iris/tests/results/cube_to_pp/append_single.txt
@@ -49,7 +49,7 @@
    bdy: -2.5
    bzx: -3.75
    bdx: 3.75
-   bmdi: -1e+30
+   bmdi: 9999.0
    bmks: 1.0
    data: [[ 254.64399719  254.64399719  254.64399719 ...,  254.64399719
    254.64399719  254.64399719]
@@ -115,7 +115,7 @@
    bdy: -2.5
    bzx: -3.75
    bdx: 3.75
-   bmdi: -1e+30
+   bmdi: 9999.0
    bmks: 1.0
    data: [[ 254.64399719  254.64399719  254.64399719 ...,  254.64399719
    254.64399719  254.64399719]
diff --git a/lib/iris/tests/results/cube_to_pp/replace_single.txt b/lib/iris/tests/results/cube_to_pp/replace_single.txt
index c5fdb48515..afff9c6f41 100644
--- a/lib/iris/tests/results/cube_to_pp/replace_single.txt
+++ b/lib/iris/tests/results/cube_to_pp/replace_single.txt
@@ -49,7 +49,7 @@
    bdy: -2.5
    bzx: -3.75
    bdx: 3.75
-   bmdi: -1e+30
+   bmdi: 9999.0
    bmks: 1.0
    data: [[ 254.64399719  254.64399719  254.64399719 ...,  254.64399719
    254.64399719  254.64399719]
diff --git a/lib/iris/tests/results/cube_to_pp/simple.txt b/lib/iris/tests/results/cube_to_pp/simple.txt
index c5fdb48515..afff9c6f41 100644
--- a/lib/iris/tests/results/cube_to_pp/simple.txt
+++ b/lib/iris/tests/results/cube_to_pp/simple.txt
@@ -49,7 +49,7 @@
    bdy: -2.5
    bzx: -3.75
    bdx: 3.75
-   bmdi: -1e+30
+   bmdi: 9999.0
    bmks: 1.0
    data: [[ 254.64399719  254.64399719  254.64399719 ...,  254.64399719
    254.64399719  254.64399719]
diff --git a/lib/iris/tests/results/cube_to_pp/user_rules.txt b/lib/iris/tests/results/cube_to_pp/user_rules.txt
index 9cac1047e0..e6d241aa86 100644
--- a/lib/iris/tests/results/cube_to_pp/user_rules.txt
+++ b/lib/iris/tests/results/cube_to_pp/user_rules.txt
@@ -49,7 +49,7 @@
    bdy: -2.5
    bzx: -3.75
    bdx: 3.75
-   bmdi: -1e+30
+   bmdi: 9999.0
    bmks: 1.0
    data: [[ 254.64399719  254.64399719  254.64399719 ...,  254.64399719
    254.64399719  254.64399719]
diff --git a/lib/iris/tests/test_cube_to_pp.py b/lib/iris/tests/test_cube_to_pp.py
index dab7298570..7041d4216a 100644
--- a/lib/iris/tests/test_cube_to_pp.py
+++ b/lib/iris/tests/test_cube_to_pp.py
@@ -1,4 +1,4 @@
-# (C) British Crown Copyright 2010 - 2016, Met Office
+# (C) British Crown Copyright 2010 - 2017, Met Office
 #
 # This file is part of Iris.
 #
@@ -28,12 +28,10 @@
 import cf_units
 import numpy as np
 
-import iris
 import iris.coords
 import iris.coord_systems
-import iris.fileformats.pp as ff_pp
+import iris.fileformats.pp
 from iris.fileformats.pp import PPField3
-import iris.io
 from iris.tests import mock
 import iris.tests.pp as pp
 import iris.util
@@ -207,12 +205,14 @@ def test_365_calendar_export(self):
         new_unit = cf_units.Unit('hours since 1970-01-01 00:00:00',
                                   calendar=cf_units.CALENDAR_365_DAY)
         cube.coord('time').units = new_unit
+        # Add an extra "fill_value" property, as used by the save rules.
+        cube.fill_value = None
         pp_field = mock.MagicMock(spec=PPField3)
         iris.fileformats.pp._ensure_save_rules_loaded()
         iris.fileformats.pp._save_rules.verify(cube, pp_field)
         self.assertEqual(pp_field.lbtim.ic, 4)
 
-            
+
 class FakePPEnvironment(object):
     ''' fake a minimal PP environment for use in cross-section coords, as in PP save rules '''
     y = [1, 2, 3, 4]
@@ -340,7 +340,7 @@ def fields_from_cube(cubes):
         fh.seek(0)
         
         # load in the saved pp fields and check the appropriate metadata
-        for field in ff_pp.load(tmp_file.name):
+        for field in iris.fileformats.pp.load(tmp_file.name):
             yield field
             
 
diff --git a/lib/iris/tests/unit/fileformats/pp/test_as_pairs.py b/lib/iris/tests/unit/fileformats/pp/test_as_pairs.py
index 6f21c2f8b0..391338d043 100644
--- a/lib/iris/tests/unit/fileformats/pp/test_as_pairs.py
+++ b/lib/iris/tests/unit/fileformats/pp/test_as_pairs.py
@@ -1,4 +1,4 @@
-# (C) British Crown Copyright 2015, Met Office
+# (C) British Crown Copyright 2015 - 2017, Met Office
 #
 # This file is part of Iris.
 #
@@ -48,6 +48,15 @@ def test_field_coords(self):
             self.assertEqual(aslice.shape, (11, 9))
             self.assertEqual(field.lbcode, 101)
 
+    def test_lazy_data(self):
+        cube = self.cube.copy()
+        # "Rebase" the cube onto a lazy version of its data.
+        cube.lazy_data(cube.lazy_data())
+        # Check that lazy data is preserved in save-pairs generation.
+        slices_and_fields = pp.as_pairs(cube)
+        for aslice, _ in slices_and_fields:
+            self.assertTrue(aslice.has_lazy_data())
+
 
 if __name__ == "__main__":
     tests.main()