diff --git a/openmc/region.py b/openmc/region.py
index 667cee5e04..9d821f93bb 100644
--- a/openmc/region.py
+++ b/openmc/region.py
@@ -61,7 +61,7 @@ class Region(object):
             Dictionary mapping surface IDs to :class:`openmc.Surface` instances
 
         """
-        if not surfaces:
+        if surfaces is None:
             surfaces = OrderedDict()
         for region in self:
             surfaces = region.update_surfaces(surfaces)
@@ -468,7 +468,7 @@ class Complement(Region):
             Dictionary mapping surface IDs to :class:`openmc.Surface` instances
 
         """
-        if not surfaces:
+        if surfaces is None:
             surfaces = OrderedDict()
         for region in self.node:
             surfaces = region.update_surfaces(surfaces)
diff --git a/openmc/surface.py b/openmc/surface.py
index 25ab4519fa..7cbd7befd3 100644
--- a/openmc/surface.py
+++ b/openmc/surface.py
@@ -1896,7 +1896,7 @@ class Halfspace(Region):
             Dictionary mapping surface IDs to :class:`openmc.Surface` instances
     
         """
-        if not surfaces:
+        if surfaces is None:
             surfaces = OrderedDict()
         
         surfaces[self.surface.id] = self.surface