diff --git a/astroplan/constraints.py b/astroplan/constraints.py
index edbf375b..630a1252 100644
--- a/astroplan/constraints.py
+++ b/astroplan/constraints.py
@@ -423,7 +423,7 @@ def _get_solar_altitudes(self, times, observer, targets):
         if not hasattr(observer, '_altaz_cache'):
             observer._altaz_cache = {}
 
-        aakey = _make_cache_key(times, "sun")
+        aakey = _make_cache_key(times, 'sun')
 
         if aakey not in observer._altaz_cache:
             try:
@@ -510,7 +510,7 @@ def compute_constraint(self, times, observer, targets):
         # centred frame, so the separation is as-seen
         # by the observer.
         # 'get_sun' returns ICRS coords.
-        sun = observer.get_body("sun", times)
+        sun = observer.get_body('sun', times)
         targets = get_skycoord(targets)
         solar_separation = sun.separation(targets)