diff --git a/lib/iris/plot.py b/lib/iris/plot.py
index f0dfccd8c5..e3193e96a4 100644
--- a/lib/iris/plot.py
+++ b/lib/iris/plot.py
@@ -317,13 +317,14 @@ def _check_bounds_contiguity_and_mask(coord, data, atol=None):
 
     elif coord.ndim == 2:
         if atol:
-            args = {'atol': atol}
+            kwargs = {'atol': atol}
         else:
-            args = {}
-        contiguous, diffs = coord._discontiguity_in_bounds(*args)
-        diffs_along_x, diffs_along_y = diffs
+            kwargs = {}
+        contiguous, diffs = coord._discontiguity_in_bounds(**kwargs)
 
         if not contiguous and data_is_masked:
+            diffs_along_x, diffs_along_y = diffs
+
             # Check along both dimensions.
             not_masked_at_discontiguity_along_x = np.any(
                 np.logical_and(mask_invert[:, :-1], diffs_along_x))
diff --git a/lib/iris/tests/unit/coords/test_Coord.py b/lib/iris/tests/unit/coords/test_Coord.py
index 58fc3e1f9e..8cf79caad3 100644
--- a/lib/iris/tests/unit/coords/test_Coord.py
+++ b/lib/iris/tests/unit/coords/test_Coord.py
@@ -504,6 +504,16 @@ def test_2d_discontiguous_along_x_and_y(self):
         self.assertArrayEqual(diffs_along_x, exp_x_diffs)
         self.assertArrayEqual(diffs_along_y, exp_y_diffs)
 
+    def test_2d_contiguous_along_x_atol(self):
+        coord = AuxCoord(self.points_3by3[:, ::2],
+                         bounds=self.lon_bounds_3by3[:, ::2, :])
+        # Set a high atol that allows small discontiguities.
+        contiguous, diffs = coord._discontiguity_in_bounds(atol=2)
+        diffs_along_x, diffs_along_y = diffs
+        self.assertTrue(contiguous)
+        self.assertArrayEqual(diffs_along_x, np.array([2, 2, 2]).reshape(3, 1))
+        self.assertTrue(not diffs_along_y.any())
+
     def test_2d_one_cell(self):
         # Test a 2D coord with a single cell, where the coord has shape (1, 1).
         coord = AuxCoord(self.points_3by3[:1, :1],
diff --git a/lib/iris/tests/unit/plot/test__check_bounds_contiguity_and_mask.py b/lib/iris/tests/unit/plot/test__check_bounds_contiguity_and_mask.py
index b067b3f387..225aa2890e 100644
--- a/lib/iris/tests/unit/plot/test__check_bounds_contiguity_and_mask.py
+++ b/lib/iris/tests/unit/plot/test__check_bounds_contiguity_and_mask.py
@@ -24,6 +24,8 @@
 # importing anything else.
 import iris.tests as tests
 
+import mock
+
 import numpy as np
 import numpy.ma as ma
 
@@ -72,6 +74,19 @@ def test_2d_contiguous(self):
         iplt._check_bounds_contiguity_and_mask(cube.coord('longitude'),
                                                cube.data)
 
+    def test_2d_contiguous_atol(self):
+        # Check the atol is passed correctly.
+        cube = sample_2d_latlons()
+        with mock.patch('iris.coords.Coord._discontiguity_in_bounds'
+                        ) as discontiguity_check:
+            # Discontiguity returns two objects that are unpacked in
+            # `_check_bounds_contiguity_and_mask`.
+            discontiguity_check.return_value = [True, None]
+            iplt._check_bounds_contiguity_and_mask(cube.coord('longitude'),
+                                                   cube.data,
+                                                   atol=1e-3)
+        discontiguity_check.assert_called_with(atol=1e-3)
+
     def test_2d_discontigous_masked(self):
         # Test a 2D coordinate which is discontiguous but masked at
         # discontiguities.