diff --git a/docs/sphinx/source/whatsnew/v0.6.0.rst b/docs/sphinx/source/whatsnew/v0.6.0.rst
index 009f015e62..1aa535c477 100644
--- a/docs/sphinx/source/whatsnew/v0.6.0.rst
+++ b/docs/sphinx/source/whatsnew/v0.6.0.rst
@@ -59,7 +59,8 @@ Bug fixes
   Location.get_clearsky. Fixed. (:issue:`481`)
 * Add User-Agent specification to TMY3 remote requests to avoid rejection.
   (:issue:`493`)
-
+* Fix ``pvlib.irradiance.klucher`` output is different for Pandas Series vs.
+  floats and NumPy arrays. (:issue:`508`)
 
 Documentation
 ~~~~~~~~~~~~~
diff --git a/pvlib/irradiance.py b/pvlib/irradiance.py
index fd03c3ffac..30060714f7 100644
--- a/pvlib/irradiance.py
+++ b/pvlib/irradiance.py
@@ -629,7 +629,7 @@ def klucher(surface_tilt, surface_azimuth, dhi, ghi, solar_zenith,
         # fails with single point input
         F.fillna(0, inplace=True)
     except AttributeError:
-        F = 0
+        F = np.where(np.isnan(F), 0, F)
 
     term1 = 0.5 * (1 + tools.cosd(surface_tilt))
     term2 = 1 + F * (tools.sind(0.5 * surface_tilt) ** 3)
diff --git a/pvlib/test/test_irradiance.py b/pvlib/test/test_irradiance.py
index ef9599e7b2..31ebbcb532 100644
--- a/pvlib/test/test_irradiance.py
+++ b/pvlib/test/test_irradiance.py
@@ -114,8 +114,20 @@ def test_isotropic_series():
 
 
 def test_klucher_series_float():
-    result = irradiance.klucher(40, 180, 100, 900, 20, 180)
-    assert_allclose(result, 88.3022221559)
+    # klucher inputs
+    surface_tilt, surface_azimuth = 40.0, 180.0
+    dhi, ghi = 100.0, 900.0
+    solar_zenith, solar_azimuth = 20.0, 180.0
+    # expect same result for floats and pd.Series
+    expected = irradiance.klucher(
+        surface_tilt, surface_azimuth,
+        pd.Series(dhi), pd.Series(ghi),
+        pd.Series(solar_zenith), pd.Series(solar_azimuth)
+    )  # 94.99429931664851
+    result = irradiance.klucher(
+        surface_tilt, surface_azimuth, dhi, ghi, solar_zenith, solar_azimuth
+    )
+    assert_allclose(result, expected[0])
 
 
 def test_klucher_series():
@@ -123,6 +135,12 @@ def test_klucher_series():
                        ephem_data['apparent_zenith'],
                        ephem_data['azimuth'])
     assert_allclose(result, [0, 37.446276, 109.209347, 56.965916], atol=1e-4)
+    # expect same result for np.array and pd.Series
+    expected = irradiance.klucher(
+        40, 180, irrad_data['dhi'].values, irrad_data['ghi'].values,
+        ephem_data['apparent_zenith'].values, ephem_data['azimuth'].values
+    )
+    assert_allclose(result, expected, atol=1e-4)
 
 
 def test_haydavies():