diff --git a/lunarsky/time.py b/lunarsky/time.py
index cf2d8f6..c786880 100644
--- a/lunarsky/time.py
+++ b/lunarsky/time.py
@@ -53,7 +53,7 @@ def __init__(
 
     def sidereal_time(self, kind, longitude=None, model=None):
         # Currently returns the zenith RA as the LST.
-        if self.location is None or self.location is EarthLocation:
+        if self.location is None or isinstance(self.location, EarthLocation):
             return super().sidereal_time(kind, longitude=longitude, model=model)
 
         if model is not None:
diff --git a/lunarsky/topo.py b/lunarsky/topo.py
index 52bc3bf..d45def0 100644
--- a/lunarsky/topo.py
+++ b/lunarsky/topo.py
@@ -125,6 +125,9 @@ def make_transform(coo, toframe):
         obstime = toframe.obstime
         location = toframe.location
 
+    if location is None:
+        raise ValueError("location must be defined for LunarTopo transformations")
+
     # Initialize station_ids if not defined.
     if location.station_ids == []:
         location.__class__._set_site_id(location)