diff --git a/docs/sphinx/source/whatsnew/v0.6.0.rst b/docs/sphinx/source/whatsnew/v0.6.0.rst
index c116fb18c5..7458e3f017 100644
--- a/docs/sphinx/source/whatsnew/v0.6.0.rst
+++ b/docs/sphinx/source/whatsnew/v0.6.0.rst
@@ -93,6 +93,9 @@ Enhancements
 * Add PVSyst thin-film recombination losses for CdTe and a:Si (:issue:`163`)
 * Python 3.7 officially supported. (:issue:`496`)
 * Improve performance of solarposition.ephemeris. (:issue:`512`)
+* Improve performance of Location.get_airmass. Most noticeable when
+  solar position is supplied, time index length is less than 10000, and
+  method is looped over. (:issue:`502`)
 
 
 Bug fixes
diff --git a/pvlib/location.py b/pvlib/location.py
index 1404bb18b0..df02858641 100644
--- a/pvlib/location.py
+++ b/pvlib/location.py
@@ -271,7 +271,7 @@ def get_airmass(self, times=None, solar_position=None,
         airmass_absolute = atmosphere.get_absolute_airmass(airmass_relative,
                                                            pressure)
 
-        airmass = pd.DataFrame()
+        airmass = pd.DataFrame(index=solar_position.index)
         airmass['airmass_relative'] = airmass_relative
         airmass['airmass_absolute'] = airmass_absolute
 
diff --git a/pvlib/modelchain.py b/pvlib/modelchain.py
index f9beeb684e..0b6f184847 100644
--- a/pvlib/modelchain.py
+++ b/pvlib/modelchain.py
@@ -736,7 +736,7 @@ def prepare_inputs(self, times=None, weather=None):
         if weather is not None:
             self.weather = weather
         if self.weather is None:
-            self.weather = pd.DataFrame()
+            self.weather = pd.DataFrame(index=times)
 
         if times is not None:
             self.times = times