diff --git a/esmvalcore/preprocessor/_derive/rsnstcsnorm.py b/esmvalcore/preprocessor/_derive/rsnstcsnorm.py
index 2f4d2241e0..62b923cef2 100644
--- a/esmvalcore/preprocessor/_derive/rsnstcsnorm.py
+++ b/esmvalcore/preprocessor/_derive/rsnstcsnorm.py
@@ -5,7 +5,7 @@
 
 """
 from iris import Constraint
-
+from cf_units import Unit
 from ._baseclass import DerivedVariableBase
 
 
@@ -53,5 +53,6 @@ def calculate(cubes):
 
         rsnstcsnorm_cube = (((rsdt_cube - rsutcs_cube) -
                              (rsdscs_cube - rsuscs_cube)) / rsdt_cube) * 100.0
+        rsnstcsnorm_cube.units = Unit('percent')
 
         return rsnstcsnorm_cube
diff --git a/tests/unit/preprocessor/_derive/test_rsntcsnorm.py b/tests/unit/preprocessor/_derive/test_rsntcsnorm.py
new file mode 100644
index 0000000000..dfe95b13ef
--- /dev/null
+++ b/tests/unit/preprocessor/_derive/test_rsntcsnorm.py
@@ -0,0 +1,39 @@
+"""Test derivation of `rsntcs`."""
+import iris
+import numpy as np
+import pytest
+
+import esmvalcore.preprocessor._derive.rsnstcsnorm as rsnstcsnorm
+
+
+@pytest.fixture
+def cubes():
+    # names
+    rsdscs_name = \
+        'surface_downwelling_shortwave_flux_in_air_assuming_clear_sky'
+    rsdt_name = 'toa_incoming_shortwave_flux'
+    rsuscs_name = 'surface_upwelling_shortwave_flux_in_air_assuming_clear_sky'
+    rsutcs_name = 'toa_outgoing_shortwave_flux_assuming_clear_sky'
+
+    # cubes
+    rsdscs_cube = iris.cube.Cube([[1.0, 2.0], [0.0, -2.0]],
+                                 standard_name=rsdscs_name)
+    rsdt_cube = iris.cube.Cube([[1.0, 2.0], [2.0, -2.0]],
+                               standard_name=rsdt_name)
+    rsuscs_cube = iris.cube.Cube([[1.0, 2.0], [0.0, -2.0]],
+                                 standard_name=rsuscs_name)
+    rsutcs_cube = iris.cube.Cube([[5.0, -1.2], [0.8, -3.0]],
+                                 standard_name=rsutcs_name)
+    return iris.cube.CubeList([rsdscs_cube, rsdt_cube,
+                               rsuscs_cube, rsutcs_cube])
+
+
+def test_rsntcs_calculation(cubes):
+    # Actual derivation of rsnstcsnorm
+    # rsnstcsnorm_cube = (((rsdt_cube - rsutcs_cube) -
+    #                      (rsdscs_cube - rsuscs_cube)) / rsdt_cube) * 100.0
+    derived_var = rsnstcsnorm.DerivedVariable()
+    out_cube = derived_var.calculate(cubes)
+    np.testing.assert_allclose(out_cube.data,
+                               np.array([[-400.,  160.], [60., -50.0]]))
+    assert out_cube.units == '%'